IOS成长之路-DES+Base64 加密、解密

DES是一种分组数据加密技术（先将数据分成固定长度的小数据块，之后进行加密），速度较快，适用于大量数据加密
3DES是一种基于DES的加密算法，使用3个不同密匙对同一个分组数据块进行3次加密，如此以使得密文强度更高。
相较于DES和3DES算法而言，AES算法有着更高的速度和资源使用效率，安全级别也较之更高了，被称为下一代加密标准。

用DES实现加密和解密的过程：（注释是我自己理解添加。不对的地方望指出）

.h文件中：

 + (NSString *)encryptWithText:(NSString *)sText;//加密
 + (NSString *)decryptWithText:(NSString *)sText;//解密

.m文件中  （导包： #import "GTMBase64.h"（下面说）   #import <CommonCrypto/CommonCryptor.h> ）

 + (NSString *)encryptWithText:(NSString *)sText
 {
     //kCCEncrypt 加密
     return [self encrypt:sText encryptOrDecrypt:kCCEncrypt key:@"des"];
 }

 + (NSString *)decryptWithText:(NSString *)sText
 {
     //kCCDecrypt 解密
     return [self encrypt:sText encryptOrDecrypt:kCCDecrypt key:@"des"];
 }

 + (NSString *)encrypt:(NSString *)sText encryptOrDecrypt:(CCOperation)encryptOperation key:(NSString *)key
 {
     const void *dataIn;
     size_t dataInLength;

     if (encryptOperation == kCCDecrypt)//传递过来的是decrypt 解码
     {
         //解码 base64
         NSData *decryptData = [GTMBase64 decodeData:[sText dataUsingEncoding:NSUTF8StringEncoding]];//转成utf-8并decode
         dataInLength = [decryptData length];
         dataIn = [decryptData bytes];
     }
     else  //encrypt
     {
         NSData* encryptData = [sText dataUsingEncoding:NSUTF8StringEncoding];
         dataInLength = [encryptData length];
         dataIn = (const void *)[encryptData bytes];
     }

     /*
      DES加密 ：用CCCrypt函数加密一下，然后用base64编码下，传过去
      DES解密 ：把收到的数据根据base64，decode一下，然后再用CCCrypt函数解密，得到原本的数据
      */
     CCCryptorStatus ccStatus;
     uint8_t *dataOut = NULL; //可以理解位type/typedef 的缩写（有效的维护了代码，比如：一个人用int，一个人用long。最好用typedef来定义）
     size_t dataOutAvailable = 0; //size_t  是操作符sizeof返回的结果类型
     size_t dataOutMoved = 0;

     dataOutAvailable = (dataInLength + kCCBlockSizeDES) & ~(kCCBlockSizeDES - 1);
     dataOut = malloc( dataOutAvailable * sizeof(uint8_t));
     memset((void *)dataOut, 0x0, dataOutAvailable);//将已开辟内存空间buffer的首 1 个字节的值设为值 0

     NSString *initIv = @"12345678";
     const void *vkey = (const void *) [key UTF8String];
     const void *iv = (const void *) [initIv UTF8String];

     //CCCrypt函数 加密/解密
     ccStatus = CCCrypt(encryptOperation,//  加密/解密
                        kCCAlgorithmDES,//  加密根据哪个标准（des，3des，aes。。。。）
                        kCCOptionPKCS7Padding,//  选项分组密码算法(des:对每块分组加一次密  3DES：对每块分组加三个不同的密)
                        vkey,  //密钥    加密和解密的密钥必须一致
                        kCCKeySizeDES,//   DES 密钥的大小（kCCKeySizeDES=8）
                        iv, //  可选的初始矢量
                        dataIn, // 数据的存储单元
                        dataInLength,// 数据的大小
                        (void *)dataOut,// 用于返回数据
                        dataOutAvailable,
                        &dataOutMoved);

     NSString *result = nil;

     if (encryptOperation == kCCDecrypt)//encryptOperation==1  解码
     {
         //得到解密出来的data数据，改变为utf-8的字符串
         result = [[[NSString alloc] initWithData:[NSData dataWithBytes:(const void *)dataOut length:(NSUInteger)dataOutMoved] encoding:NSUTF8StringEncoding] autorelease];
     }
     else //encryptOperation==0  （加密过程中，把加好密的数据转成base64的）
     {
         //编码 base64
         NSData *data = [NSData dataWithBytes:(const void *)dataOut length:(NSUInteger)dataOutMoved];
         result = [GTMBase64 stringByEncodingData:data];
     }

     return result;
 }

这里用到了Base64.。。从网上找到了一些好的类，直接贴到这里用

Base64.h

 //
 //  GTMBase64.h
 //
 //  Copyright 2006-2008 Google Inc.
 //
 //  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 //  use this file except in compliance with the License.  You may obtain a copy
 //  of the License at
 //
 //  http://www.apache.org/licenses/LICENSE-2.0
 //
 //  Unless required by applicable law or agreed to in writing, software
 //  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 //  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 //  License for the specific language governing permissions and limitations under
 //  the License.
 //

 #import <Foundation/Foundation.h>
 #import "GTMDefines.h"

 // GTMBase64
 //
 /// Helper for handling Base64 and WebSafeBase64 encodings
 //
 /// The webSafe methods use different character set and also the results aren't
 /// always padded to a multiple of 4 characters.  This is done so the resulting
 /// data can be used in urls and url query arguments without needing any
 /// encoding.  You must use the webSafe* methods together, the data does not
 /// interop with the RFC methods.
 //
 @interface GTMBase64 : NSObject

 //
 // Standard Base64 (RFC) handling
 //

 // encodeData:
 //
 /// Base64 encodes contents of the NSData object.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)encodeData:(NSData *)data;

 // decodeData:
 //
 /// Base64 decodes contents of the NSData object.
 //
 /// Returns:
 ///   A new autoreleased NSData with the decoded payload.  nil for any error.
 //
 +(NSData *)decodeData:(NSData *)data;

 // encodeBytes:length:
 //
 /// Base64 encodes the data pointed at by |bytes|.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)encodeBytes:(const void *)bytes length:(NSUInteger)length;

 // decodeBytes:length:
 //
 /// Base64 decodes the data pointed at by |bytes|.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)decodeBytes:(const void *)bytes length:(NSUInteger)length;

 // stringByEncodingData:
 //
 /// Base64 encodes contents of the NSData object.
 //
 /// Returns:
 ///   A new autoreleased NSString with the encoded payload.  nil for any error.
 //
 +(NSString *)stringByEncodingData:(NSData *)data;

 // stringByEncodingBytes:length:
 //
 /// Base64 encodes the data pointed at by |bytes|.
 //
 /// Returns:
 ///   A new autoreleased NSString with the encoded payload.  nil for any error.
 //
 +(NSString *)stringByEncodingBytes:(const void *)bytes length:(NSUInteger)length;

 // decodeString:
 //
 /// Base64 decodes contents of the NSString.
 //
 /// Returns:
 ///   A new autoreleased NSData with the decoded payload.  nil for any error.
 //
 +(NSData *)decodeString:(NSString *)string;

 //
 // Modified Base64 encoding so the results can go onto urls.
 //
 // The changes are in the characters generated and also allows the result to
 // not be padded to a multiple of 4.
 // Must use the matching call to encode/decode, won't interop with the
 // RFC versions.
 //

 // webSafeEncodeData:padded:
 //
 /// WebSafe Base64 encodes contents of the NSData object.  If |padded| is YES
 /// then padding characters are added so the result length is a multiple of 4.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)webSafeEncodeData:(NSData *)data
                       padded:(BOOL)padded;

 // webSafeDecodeData:
 //
 /// WebSafe Base64 decodes contents of the NSData object.
 //
 /// Returns:
 ///   A new autoreleased NSData with the decoded payload.  nil for any error.
 //
 +(NSData *)webSafeDecodeData:(NSData *)data;

 // webSafeEncodeBytes:length:padded:
 //
 /// WebSafe Base64 encodes the data pointed at by |bytes|.  If |padded| is YES
 /// then padding characters are added so the result length is a multiple of 4.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)webSafeEncodeBytes:(const void *)bytes
                        length:(NSUInteger)length
                        padded:(BOOL)padded;

 // webSafeDecodeBytes:length:
 //
 /// WebSafe Base64 decodes the data pointed at by |bytes|.
 //
 /// Returns:
 ///   A new autoreleased NSData with the encoded payload.  nil for any error.
 //
 +(NSData *)webSafeDecodeBytes:(const void *)bytes length:(NSUInteger)length;

 // stringByWebSafeEncodingData:padded:
 //
 /// WebSafe Base64 encodes contents of the NSData object.  If |padded| is YES
 /// then padding characters are added so the result length is a multiple of 4.
 //
 /// Returns:
 ///   A new autoreleased NSString with the encoded payload.  nil for any error.
 //
 +(NSString *)stringByWebSafeEncodingData:(NSData *)data
                                   padded:(BOOL)padded;

 // stringByWebSafeEncodingBytes:length:padded:
 //
 /// WebSafe Base64 encodes the data pointed at by |bytes|.  If |padded| is YES
 /// then padding characters are added so the result length is a multiple of 4.
 //
 /// Returns:
 ///   A new autoreleased NSString with the encoded payload.  nil for any error.
 //
 +(NSString *)stringByWebSafeEncodingBytes:(const void *)bytes
                                    length:(NSUInteger)length
                                    padded:(BOOL)padded;

 // webSafeDecodeString:
 //
 /// WebSafe Base64 decodes contents of the NSString.
 //
 /// Returns:
 ///   A new autoreleased NSData with the decoded payload.  nil for any error.
 //
 +(NSData *)webSafeDecodeString:(NSString *)string;

 @end

Base64.m

 //
 //  GTMBase64.m
 //
 //  Copyright 2006-2008 Google Inc.
 //
 //  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 //  use this file except in compliance with the License.  You may obtain a copy
 //  of the License at
 //
 //  http://www.apache.org/licenses/LICENSE-2.0
 //
 //  Unless required by applicable law or agreed to in writing, software
 //  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 //  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 //  License for the specific language governing permissions and limitations under
 //  the License.
 //

 #import "GTMBase64.h"
 #import "GTMDefines.h"

 static const char *kBase64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 static const char *kWebSafeBase64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
 static const char kBase64PaddingChar = '=';
 static const char kBase64InvalidChar = 99;

 static const char kBase64DecodeChars[] = {
     // This array was generated by the following code:
     // #include <sys/time.h>
     // #include <stdlib.h>
     // #include <string.h>
     // main()
     // {
     //   static const char Base64[] =
     //     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
     //   char *pos;
     //   int idx, i, j;
     //   printf("    ");
     //   for (i = 0; i < 255; i += 8) {
     //     for (j = i; j < i + 8; j++) {
     //       pos = strchr(Base64, j);
     //       if ((pos == NULL) || (j == 0))
     //         idx = 99;
     //       else
     //         idx = pos - Base64;
     //       if (idx == 99)
     //         printf(" %2d,     ", idx);
     //       else
     //         printf(" %2d/*%c*/,", idx, j);
     //     }
     //     printf("\n    ");
     //   }
     // }
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      62/*+*/, 99,      99,      99,      63/*/ */,
     52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
     60/*8*/, 61/*9*/, 99,      99,      99,      99,      99,      99,
     99,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
     7/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
     15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
     23/*X*/, 24/*Y*/, 25/*Z*/, 99,      99,      99,      99,      99,
     99,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
     33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
     41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
     49/*x*/, 50/*y*/, 51/*z*/, 99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99
 };

 static const char kWebSafeBase64DecodeChars[] = {
     // This array was generated by the following code:
     // #include <sys/time.h>
     // #include <stdlib.h>
     // #include <string.h>
     // main()
     // {
     //   static const char Base64[] =
     //     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
     //   char *pos;
     //   int idx, i, j;
     //   printf("    ");
     //   for (i = 0; i < 255; i += 8) {
     //     for (j = i; j < i + 8; j++) {
     //       pos = strchr(Base64, j);
     //       if ((pos == NULL) || (j == 0))
     //         idx = 99;
     //       else
     //         idx = pos - Base64;
     //       if (idx == 99)
     //         printf(" %2d,     ", idx);
     //       else
     //         printf(" %2d/*%c*/,", idx, j);
     //     }
     //     printf("\n    ");
     //   }
     // }
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      62/*-*/, 99,      99,
     52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
     60/*8*/, 61/*9*/, 99,      99,      99,      99,      99,      99,
     99,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
     7/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
     15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
     23/*X*/, 24/*Y*/, 25/*Z*/, 99,      99,      99,      99,      63/*_*/,
     99,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
     33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
     41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
     49/*x*/, 50/*y*/, 51/*z*/, 99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99,
     99,      99,      99,      99,      99,      99,      99,      99
 };


 // Tests a charact to see if it's a whitespace character.
 //
 // Returns:
 //   YES if the character is a whitespace character.
 //   NO if the character is not a whitespace character.
 //
 FOUNDATION_STATIC_INLINE BOOL IsSpace(unsigned char c) {
     // we use our own mapping here because we don't want anything w/ locale
     // support.
     static BOOL kSpaces[256] = {
         0, 0, 0, 0, 0, 0, 0, 0, 0, 1,  // 0-9
         1, 1, 1, 1, 0, 0, 0, 0, 0, 0,  // 10-19
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 20-29
         0, 0, 1, 0, 0, 0, 0, 0, 0, 0,  // 30-39
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 40-49
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 50-59
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 60-69
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 70-79
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 80-89
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 90-99
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 100-109
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 110-119
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 120-129
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 130-139
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 140-149
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 150-159
         1, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 160-169
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 170-179
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 180-189
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 190-199
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 200-209
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 210-219
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 220-229
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 230-239
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 240-249
         0, 0, 0, 0, 0, 1,              // 250-255
     };
     return kSpaces[c];
 }

 // Calculate how long the data will be once it's base64 encoded.
 //
 // Returns:
 //   The guessed encoded length for a source length
 //
 FOUNDATION_STATIC_INLINE NSUInteger CalcEncodedLength(NSUInteger srcLen,
                                                       BOOL padded) {
     NSUInteger intermediate_result = 8 * srcLen + 5;
     NSUInteger len = intermediate_result / 6;
     if (padded) {
         len = ((len + 3) / 4) * 4;
     }
     return len;
 }

 // Tries to calculate how long the data will be once it's base64 decoded.
 // Unlinke the above, this is always an upperbound, since the source data
 // could have spaces and might end with the padding characters on them.
 //
 // Returns:
 //   The guessed decoded length for a source length
 //
 FOUNDATION_STATIC_INLINE NSUInteger GuessDecodedLength(NSUInteger srcLen) {
     return (srcLen + 3) / 4 * 3;
 }


 @interface GTMBase64 (PrivateMethods)

 +(NSData *)baseEncode:(const void *)bytes
                length:(NSUInteger)length
               charset:(const char *)charset
                padded:(BOOL)padded;

 +(NSData *)baseDecode:(const void *)bytes
                length:(NSUInteger)length
               charset:(const char*)charset
        requirePadding:(BOOL)requirePadding;

 +(NSUInteger)baseEncode:(const char *)srcBytes
                  srcLen:(NSUInteger)srcLen
               destBytes:(char *)destBytes
                 destLen:(NSUInteger)destLen
                 charset:(const char *)charset
                  padded:(BOOL)padded;

 +(NSUInteger)baseDecode:(const char *)srcBytes
                  srcLen:(NSUInteger)srcLen
               destBytes:(char *)destBytes
                 destLen:(NSUInteger)destLen
                 charset:(const char *)charset
          requirePadding:(BOOL)requirePadding;

 @end


 @implementation GTMBase64

 //
 // Standard Base64 (RFC) handling
 //

 +(NSData *)encodeData:(NSData *)data {
     return [self baseEncode:[data bytes]
                      length:[data length]
                     charset:kBase64EncodeChars
                      padded:YES];
 }

 +(NSData *)decodeData:(NSData *)data {
     return [self baseDecode:[data bytes]
                      length:[data length]
                     charset:kBase64DecodeChars
              requirePadding:YES];
 }

 +(NSData *)encodeBytes:(const void *)bytes length:(NSUInteger)length {
     return [self baseEncode:bytes
                      length:length
                     charset:kBase64EncodeChars
                      padded:YES];
 }

 +(NSData *)decodeBytes:(const void *)bytes length:(NSUInteger)length {
     return [self baseDecode:bytes
                      length:length
                     charset:kBase64DecodeChars
              requirePadding:YES];
 }

 +(NSString *)stringByEncodingData:(NSData *)data {
     NSString *result = nil;
     NSData *converted = [self baseEncode:[data bytes]
                                   length:[data length]
                                  charset:kBase64EncodeChars
                                   padded:YES];
     if (converted) {
         result = [[[NSString alloc] initWithData:converted
                                         encoding:NSASCIIStringEncoding] autorelease];
     }
     return result;
 }

 +(NSString *)stringByEncodingBytes:(const void *)bytes length:(NSUInteger)length {
     NSString *result = nil;
     NSData *converted = [self baseEncode:bytes
                                   length:length
                                  charset:kBase64EncodeChars
                                   padded:YES];
     if (converted) {
         result = [[[NSString alloc] initWithData:converted
                                         encoding:NSASCIIStringEncoding] autorelease];
     }
     return result;
 }

 +(NSData *)decodeString:(NSString *)string {
     NSData *result = nil;
     NSData *data = [string dataUsingEncoding:NSASCIIStringEncoding];
     if (data) {
         result = [self baseDecode:[data bytes]
                            length:[data length]
                           charset:kBase64DecodeChars
                    requirePadding:YES];
     }
     return result;
 }

 //
 // Modified Base64 encoding so the results can go onto urls.
 //
 // The changes are in the characters generated and also the result isn't
 // padded to a multiple of 4.
 // Must use the matching call to encode/decode, won't interop with the
 // RFC versions.
 //

 +(NSData *)webSafeEncodeData:(NSData *)data
                       padded:(BOOL)padded {
     return [self baseEncode:[data bytes]
                      length:[data length]
                     charset:kWebSafeBase64EncodeChars
                      padded:padded];
 }

 +(NSData *)webSafeDecodeData:(NSData *)data {
     return [self baseDecode:[data bytes]
                      length:[data length]
                     charset:kWebSafeBase64DecodeChars
              requirePadding:NO];
 }

 +(NSData *)webSafeEncodeBytes:(const void *)bytes
                        length:(NSUInteger)length
                        padded:(BOOL)padded {
     return [self baseEncode:bytes
                      length:length
                     charset:kWebSafeBase64EncodeChars
                      padded:padded];
 }

 +(NSData *)webSafeDecodeBytes:(const void *)bytes length:(NSUInteger)length {
     return [self baseDecode:bytes
                      length:length
                     charset:kWebSafeBase64DecodeChars
              requirePadding:NO];
 }

 +(NSString *)stringByWebSafeEncodingData:(NSData *)data
                                   padded:(BOOL)padded {
     NSString *result = nil;
     NSData *converted = [self baseEncode:[data bytes]
                                   length:[data length]
                                  charset:kWebSafeBase64EncodeChars
                                   padded:padded];
     if (converted) {
         result = [[[NSString alloc] initWithData:converted
                                         encoding:NSASCIIStringEncoding] autorelease];
     }
     return result;
 }

 +(NSString *)stringByWebSafeEncodingBytes:(const void *)bytes
                                    length:(NSUInteger)length
                                    padded:(BOOL)padded {
     NSString *result = nil;
     NSData *converted = [self baseEncode:bytes
                                   length:length
                                  charset:kWebSafeBase64EncodeChars
                                   padded:padded];
     if (converted) {
         result = [[[NSString alloc] initWithData:converted
                                         encoding:NSASCIIStringEncoding] autorelease];
     }
     return result;
 }

 +(NSData *)webSafeDecodeString:(NSString *)string {
     NSData *result = nil;
     NSData *data = [string dataUsingEncoding:NSASCIIStringEncoding];
     if (data) {
         result = [self baseDecode:[data bytes]
                            length:[data length]
                           charset:kWebSafeBase64DecodeChars
                    requirePadding:NO];
     }
     return result;
 }

 @end

 @implementation GTMBase64 (PrivateMethods)

 //
 // baseEncode:length:charset:padded:
 //
 // Does the common lifting of creating the dest NSData.  it creates & sizes the
 // data for the results.  |charset| is the characters to use for the encoding
 // of the data.  |padding| controls if the encoded data should be padded to a
 // multiple of 4.
 //
 // Returns:
 //   an autorelease NSData with the encoded data, nil if any error.
 //
 +(NSData *)baseEncode:(const void *)bytes
                length:(NSUInteger)length
               charset:(const char *)charset
                padded:(BOOL)padded {
     // how big could it be?
     NSUInteger maxLength = CalcEncodedLength(length, padded);
     // make space
     NSMutableData *result = [NSMutableData data];
     [result setLength:maxLength];
     // do it
     NSUInteger finalLength = [self baseEncode:bytes
                                        srcLen:length
                                     destBytes:[result mutableBytes]
                                       destLen:[result length]
                                       charset:charset
                                        padded:padded];
     if (finalLength) {
         _GTMDevAssert(finalLength == maxLength, @"how did we calc the length wrong?");
     } else {
         // shouldn't happen, this means we ran out of space
         result = nil;
     }
     return result;
 }

 //
 // baseDecode:length:charset:requirePadding:
 //
 // Does the common lifting of creating the dest NSData.  it creates & sizes the
 // data for the results.  |charset| is the characters to use for the decoding
 // of the data.
 //
 // Returns:
 //   an autorelease NSData with the decoded data, nil if any error.
 //
 //
 +(NSData *)baseDecode:(const void *)bytes
                length:(NSUInteger)length
               charset:(const char *)charset
        requirePadding:(BOOL)requirePadding {
     // could try to calculate what it will end up as
     NSUInteger maxLength = GuessDecodedLength(length);
     // make space
     NSMutableData *result = [NSMutableData data];
     [result setLength:maxLength];
     // do it
     NSUInteger finalLength = [self baseDecode:bytes
                                        srcLen:length
                                     destBytes:[result mutableBytes]
                                       destLen:[result length]
                                       charset:charset
                                requirePadding:requirePadding];
     if (finalLength) {
         if (finalLength != maxLength) {
             // resize down to how big it was
             [result setLength:finalLength];
         }
     } else {
         // either an error in the args, or we ran out of space
         result = nil;
     }
     return result;
 }

 //
 // baseEncode:srcLen:destBytes:destLen:charset:padded:
 //
 // Encodes the buffer into the larger.  returns the length of the encoded
 // data, or zero for an error.
 // |charset| is the characters to use for the encoding
 // |padded| tells if the result should be padded to a multiple of 4.
 //
 // Returns:
 //   the length of the encoded data.  zero if any error.
 //
 +(NSUInteger)baseEncode:(const char *)srcBytes
                  srcLen:(NSUInteger)srcLen
               destBytes:(char *)destBytes
                 destLen:(NSUInteger)destLen
                 charset:(const char *)charset
                  padded:(BOOL)padded {
     if (!srcLen || !destLen || !srcBytes || !destBytes) {
         return 0;
     }

     char *curDest = destBytes;
     const unsigned char *curSrc = (const unsigned char *)(srcBytes);

     // Three bytes of data encodes to four characters of cyphertext.
     // So we can pump through three-byte chunks atomically.
     while (srcLen > 2) {
         // space?
         _GTMDevAssert(destLen >= 4, @"our calc for encoded length was wrong");
         curDest[0] = charset[curSrc[0] >> 2];
         curDest[1] = charset[((curSrc[0] & 0x03) << 4) + (curSrc[1] >> 4)];
         curDest[2] = charset[((curSrc[1] & 0x0f) << 2) + (curSrc[2] >> 6)];
         curDest[3] = charset[curSrc[2] & 0x3f];

         curDest += 4;
         curSrc += 3;
         srcLen -= 3;
         destLen -= 4;
     }

     // now deal with the tail (<=2 bytes)
     switch (srcLen) {
         case 0:
             // Nothing left; nothing more to do.
             break;
         case 1:
             // One byte left: this encodes to two characters, and (optionally)
             // two pad characters to round out the four-character cypherblock.
             _GTMDevAssert(destLen >= 2, @"our calc for encoded length was wrong");
             curDest[0] = charset[curSrc[0] >> 2];
             curDest[1] = charset[(curSrc[0] & 0x03) << 4];
             curDest += 2;
             destLen -= 2;
             if (padded) {
                 _GTMDevAssert(destLen >= 2, @"our calc for encoded length was wrong");
                 curDest[0] = kBase64PaddingChar;
                 curDest[1] = kBase64PaddingChar;
                 curDest += 2;
                 destLen -= 2;
             }
             break;
         case 2:
             // Two bytes left: this encodes to three characters, and (optionally)
             // one pad character to round out the four-character cypherblock.
             _GTMDevAssert(destLen >= 3, @"our calc for encoded length was wrong");
             curDest[0] = charset[curSrc[0] >> 2];
             curDest[1] = charset[((curSrc[0] & 0x03) << 4) + (curSrc[1] >> 4)];
             curDest[2] = charset[(curSrc[1] & 0x0f) << 2];
             curDest += 3;
             destLen -= 3;
             if (padded) {
                 _GTMDevAssert(destLen >= 1, @"our calc for encoded length was wrong");
                 curDest[0] = kBase64PaddingChar;
                 curDest += 1;
                 destLen -= 1;
             }
             break;
     }
     // return the length
     return (curDest - destBytes);
 }

 //
 // baseDecode:srcLen:destBytes:destLen:charset:requirePadding:
 //
 // Decodes the buffer into the larger.  returns the length of the decoded
 // data, or zero for an error.
 // |charset| is the character decoding buffer to use
 //
 // Returns:
 //   the length of the encoded data.  zero if any error.
 //
 +(NSUInteger)baseDecode:(const char *)srcBytes
                  srcLen:(NSUInteger)srcLen
               destBytes:(char *)destBytes
                 destLen:(NSUInteger)destLen
                 charset:(const char *)charset
          requirePadding:(BOOL)requirePadding {
     if (!srcLen || !destLen || !srcBytes || !destBytes) {
         return 0;
     }

     int decode;
     NSUInteger destIndex = 0;
     int state = 0;
     char ch = 0;
     while (srcLen-- && (ch = *srcBytes++) != 0)  {
         if (IsSpace(ch))  // Skip whitespace
             continue;

         if (ch == kBase64PaddingChar)
             break;

         decode = charset[(unsigned int)ch];
         if (decode == kBase64InvalidChar)
             return 0;

         // Four cyphertext characters decode to three bytes.
         // Therefore we can be in one of four states.
         switch (state) {
             case 0:
                 // We're at the beginning of a four-character cyphertext block.
                 // This sets the high six bits of the first byte of the
                 // plaintext block.
                 _GTMDevAssert(destIndex < destLen, @"our calc for decoded length was wrong");
                 destBytes[destIndex] = decode << 2;
                 state = 1;
                 break;
             case 1:
                 // We're one character into a four-character cyphertext block.
                 // This sets the low two bits of the first plaintext byte,
                 // and the high four bits of the second plaintext byte.
                 _GTMDevAssert((destIndex+1) < destLen, @"our calc for decoded length was wrong");
                 destBytes[destIndex] |= decode >> 4;
                 destBytes[destIndex+1] = (decode & 0x0f) << 4;
                 destIndex++;
                 state = 2;
                 break;
             case 2:
                 // We're two characters into a four-character cyphertext block.
                 // This sets the low four bits of the second plaintext
                 // byte, and the high two bits of the third plaintext byte.
                 // However, if this is the end of data, and those two
                 // bits are zero, it could be that those two bits are
                 // leftovers from the encoding of data that had a length
                 // of two mod three.
                 _GTMDevAssert((destIndex+1) < destLen, @"our calc for decoded length was wrong");
                 destBytes[destIndex] |= decode >> 2;
                 destBytes[destIndex+1] = (decode & 0x03) << 6;
                 destIndex++;
                 state = 3;
                 break;
             case 3:
                 // We're at the last character of a four-character cyphertext block.
                 // This sets the low six bits of the third plaintext byte.
                 _GTMDevAssert(destIndex < destLen, @"our calc for decoded length was wrong");
                 destBytes[destIndex] |= decode;
                 destIndex++;
                 state = 0;
                 break;
         }
     }

     // We are done decoding Base-64 chars.  Let's see if we ended
     //      on a byte boundary, and/or with erroneous trailing characters.
     if (ch == kBase64PaddingChar) {               // We got a pad char
         if ((state == 0) || (state == 1)) {
             return 0;  // Invalid '=' in first or second position
         }
         if (srcLen == 0) {
             if (state == 2) { // We run out of input but we still need another '='
                 return 0;
             }
             // Otherwise, we are in state 3 and only need this '='
         } else {
             if (state == 2) {  // need another '='
                 while ((ch = *srcBytes++) && (srcLen-- > 0)) {
                     if (!IsSpace(ch))
                         break;
                 }
                 if (ch != kBase64PaddingChar) {
                     return 0;
                 }
             }
             // state = 1 or 2, check if all remain padding is space
             while ((ch = *srcBytes++) && (srcLen-- > 0)) {
                 if (!IsSpace(ch)) {
                     return 0;
                 }
             }
         }
     } else {
         // We ended by seeing the end of the string.

         if (requirePadding) {
             // If we require padding, then anything but state 0 is an error.
             if (state != 0) {
                 return 0;
             }
         } else {
             // Make sure we have no partial bytes lying around.  Note that we do not
             // require trailing '=', so states 2 and 3 are okay too.
             if (state == 1) {
                 return 0;
             }
         }
     }

     // If then next piece of output was valid and got written to it means we got a
     // very carefully crafted input that appeared valid but contains some trailing
     // bits past the real length, so just toss the thing.
     if ((destIndex < destLen) &&
         (destBytes[destIndex] != 0)) {
         return 0;
     }

     return destIndex;
 }

 @end

在Base64 代码中用到了一个.h文件

Defines.h

 //
 // GTMDefines.h
 //
 //  Copyright 2008 Google Inc.
 //
 //  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 //  use this file except in compliance with the License.  You may obtain a copy
 //  of the License at
 //
 //  http://www.apache.org/licenses/LICENSE-2.0
 //
 //  Unless required by applicable law or agreed to in writing, software
 //  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 //  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 //  License for the specific language governing permissions and limitations under
 //  the License.
 //

 // ============================================================================

 #include <AvailabilityMacros.h>

 // Not all MAC_OS_X_VERSION_10_X macros defined in past SDKs
 #ifndef MAC_OS_X_VERSION_10_5
 #define MAC_OS_X_VERSION_10_5 1050
 #endif
 #ifndef MAC_OS_X_VERSION_10_6
 #define MAC_OS_X_VERSION_10_6 1060
 #endif

 // ----------------------------------------------------------------------------
 // CPP symbols that can be overridden in a prefix to control how the toolbox
 // is compiled.
 // ----------------------------------------------------------------------------


 // GTMHTTPFetcher will support logging by default but only hook its input
 // stream support for logging when requested.  You can control the inclusion of
 // the code by providing your own definitions for these w/in a prefix header.
 //
 #ifndef GTM_HTTPFETCHER_ENABLE_LOGGING
 #define GTM_HTTPFETCHER_ENABLE_LOGGING 1
 #endif // GTM_HTTPFETCHER_ENABLE_LOGGING
 #ifndef GTM_HTTPFETCHER_ENABLE_INPUTSTREAM_LOGGING
 #define GTM_HTTPFETCHER_ENABLE_INPUTSTREAM_LOGGING 0
 #endif // GTM_HTTPFETCHER_ENABLE_INPUTSTREAM_LOGGING

 // By setting the GTM_CONTAINERS_VALIDATION_FAILED_LOG and
 // GTM_CONTAINERS_VALIDATION_FAILED_ASSERT macros you can control what happens
 // when a validation fails. If you implement your own validators, you may want
 // to control their internals using the same macros for consistency.
 #ifndef GTM_CONTAINERS_VALIDATION_FAILED_ASSERT
 #define GTM_CONTAINERS_VALIDATION_FAILED_ASSERT 0
 #endif

 // Give ourselves a consistent way to do inlines.  Apple's macros even use
 // a few different actual definitions, so we're based off of the foundation
 // one.
 #if !defined(GTM_INLINE)
 #if defined (__GNUC__) && (__GNUC__ == 4)
 #define GTM_INLINE static __inline__ __attribute__((always_inline))
 #else
 #define GTM_INLINE static __inline__
 #endif
 #endif

 // Give ourselves a consistent way of doing externs that links up nicely
 // when mixing objc and objc++
 #if !defined (GTM_EXTERN)
 #if defined __cplusplus
 #define GTM_EXTERN extern "C"
 #else
 #define GTM_EXTERN extern
 #endif
 #endif

 // Give ourselves a consistent way of exporting things if we have visibility
 // set to hidden.
 #if !defined (GTM_EXPORT)
 #define GTM_EXPORT __attribute__((visibility("default")))
 #endif

 // _GTMDevLog & _GTMDevAssert
 //
 // _GTMDevLog & _GTMDevAssert are meant to be a very lightweight shell for
 // developer level errors.  This implementation simply macros to NSLog/NSAssert.
 // It is not intended to be a general logging/reporting system.
 //
 // Please see http://code.google.com/p/google-toolbox-for-mac/wiki/DevLogNAssert
 // for a little more background on the usage of these macros.
 //
 //    _GTMDevLog           log some error/problem in debug builds
 //    _GTMDevAssert        assert if conditon isn't met w/in a method/function
 //                           in all builds.
 //
 // To replace this system, just provide different macro definitions in your
 // prefix header.  Remember, any implementation you provide *must* be thread
 // safe since this could be called by anything in what ever situtation it has
 // been placed in.
 //

 // We only define the simple macros if nothing else has defined this.
 #ifndef _GTMDevLog

 #ifdef DEBUG
 #define _GTMDevLog(...) NSLog(__VA_ARGS__)
 #else
 #define _GTMDevLog(...) do { } while (0)
 #endif

 #endif // _GTMDevLog

 // Declared here so that it can easily be used for logging tracking if
 // necessary. See GTMUnitTestDevLog.h for details.
 @class NSString;
 GTM_EXTERN void _GTMUnitTestDevLog(NSString *format, ...);

 #ifndef _GTMDevAssert
 // we directly invoke the NSAssert handler so we can pass on the varargs
 // (NSAssert doesn't have a macro we can use that takes varargs)
 #if !defined(NS_BLOCK_ASSERTIONS)
 #define _GTMDevAssert(condition, ...)                                       \
 do {                                                                      \
 if (!(condition)) {                                                     \
 [[NSAssertionHandler currentHandler]                                  \
 handleFailureInFunction:[NSString stringWithUTF8String:__PRETTY_FUNCTION__] \
 file:[NSString stringWithUTF8String:__FILE__]  \
 lineNumber:__LINE__                                  \
 description:__VA_ARGS__];                             \
 }                                                                       \
 } while(0)
 #else // !defined(NS_BLOCK_ASSERTIONS)
 #define _GTMDevAssert(condition, ...) do { } while (0)
 #endif // !defined(NS_BLOCK_ASSERTIONS)

 #endif // _GTMDevAssert

 // _GTMCompileAssert
 // _GTMCompileAssert is an assert that is meant to fire at compile time if you
 // want to check things at compile instead of runtime. For example if you
 // want to check that a wchar is 4 bytes instead of 2 you would use
 // _GTMCompileAssert(sizeof(wchar_t) == 4, wchar_t_is_4_bytes_on_OS_X)
 // Note that the second "arg" is not in quotes, and must be a valid processor
 // symbol in it's own right (no spaces, punctuation etc).

 // Wrapping this in an #ifndef allows external groups to define their own
 // compile time assert scheme.
 #ifndef _GTMCompileAssert
 // We got this technique from here:
 // http://unixjunkie.blogspot.com/2007/10/better-compile-time-asserts_29.html

 #define _GTMCompileAssertSymbolInner(line, msg) _GTMCOMPILEASSERT ## line ## __ ## msg
 #define _GTMCompileAssertSymbol(line, msg) _GTMCompileAssertSymbolInner(line, msg)
 #define _GTMCompileAssert(test, msg) \
 typedef char _GTMCompileAssertSymbol(__LINE__, msg) [ ((test) ? 1 : -1) ]
 #endif // _GTMCompileAssert

 // Macro to allow fast enumeration when building for 10.5 or later, and
 // reliance on NSEnumerator for 10.4.  Remember, NSDictionary w/ FastEnumeration
 // does keys, so pick the right thing, nothing is done on the FastEnumeration
 // side to be sure you're getting what you wanted.
 #ifndef GTM_FOREACH_OBJECT
 #if defined(TARGET_OS_IPHONE) || (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_5)
 #define GTM_FOREACH_OBJECT(element, collection) \
 for (element in collection)
 #define GTM_FOREACH_KEY(element, collection) \
 for (element in collection)
 #else
 #define GTM_FOREACH_OBJECT(element, collection) \
 for (NSEnumerator * _ ## element ## _enum = [collection objectEnumerator]; \
 (element = [_ ## element ## _enum nextObject]) != nil; )
 #define GTM_FOREACH_KEY(element, collection) \
 for (NSEnumerator * _ ## element ## _enum = [collection keyEnumerator]; \
 (element = [_ ## element ## _enum nextObject]) != nil; )
 #endif
 #endif

 // ============================================================================

 // ----------------------------------------------------------------------------
 // CPP symbols defined based on the project settings so the GTM code has
 // simple things to test against w/o scattering the knowledge of project
 // setting through all the code.
 // ----------------------------------------------------------------------------

 // Provide a single constant CPP symbol that all of GTM uses for ifdefing
 // iPhone code.
 #include <TargetConditionals.h>
 #if TARGET_OS_IPHONE // iPhone SDK
 // For iPhone specific stuff
 #define GTM_IPHONE_SDK 1
 #if TARGET_IPHONE_SIMULATOR
 #define GTM_IPHONE_SIMULATOR 1
 #else
 #define GTM_IPHONE_DEVICE 1
 #endif  // TARGET_IPHONE_SIMULATOR
 #else
 // For MacOS specific stuff
 #define GTM_MACOS_SDK 1
 #endif

 // Provide a symbol to include/exclude extra code for GC support.  (This mainly
 // just controls the inclusion of finalize methods).
 #ifndef GTM_SUPPORT_GC
 #if GTM_IPHONE_SDK
 // iPhone never needs GC
 #define GTM_SUPPORT_GC 0
 #else
 // We can't find a symbol to tell if GC is supported/required, so best we
 // do on Mac targets is include it if we're on 10.5 or later.
 #if MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_4
 #define GTM_SUPPORT_GC 0
 #else
 #define GTM_SUPPORT_GC 1
 #endif
 #endif
 #endif

 // To simplify support for 64bit (and Leopard in general), we provide the type
 // defines for non Leopard SDKs
 #if MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_4
 // NSInteger/NSUInteger and Max/Mins
 #ifndef NSINTEGER_DEFINED
 #if __LP64__ || NS_BUILD_32_LIKE_64
 typedef long NSInteger;
 typedef unsigned long NSUInteger;
 #else
 typedef int NSInteger;
 typedef unsigned int NSUInteger;
 #endif
 #define NSIntegerMax    LONG_MAX
 #define NSIntegerMin    LONG_MIN
 #define NSUIntegerMax   ULONG_MAX
 #define NSINTEGER_DEFINED 1
 #endif  // NSINTEGER_DEFINED
 // CGFloat
 #ifndef CGFLOAT_DEFINED
 #if defined(__LP64__) && __LP64__
 // This really is an untested path (64bit on Tiger?)
 typedef double CGFloat;
 #define CGFLOAT_MIN DBL_MIN
 #define CGFLOAT_MAX DBL_MAX
 #define CGFLOAT_IS_DOUBLE 1
 #else /* !defined(__LP64__) || !__LP64__ */
 typedef float CGFloat;
 #define CGFLOAT_MIN FLT_MIN
 #define CGFLOAT_MAX FLT_MAX
 #define CGFLOAT_IS_DOUBLE 0
 #endif /* !defined(__LP64__) || !__LP64__ */
 #define CGFLOAT_DEFINED 1
 #endif // CGFLOAT_DEFINED
 #endif  // MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_4

调用方法测试：

 NSString *encrypt = [ViewController encryptWithText:@"中华人民共和国万岁！！"];
     NSLog(@"enctry = %@",encrypt);
     NSString *decrypt = [ViewController decryptWithText:encrypt];
     NSLog(@"decrypt = %@",decrypt);

输出结果：

enctry = IKnyVPAK8eprKHHunG7Ze9tTfU8sIoYho8SFeyFEniK/7wy3u7stKA==

decrypt =中华人民共和国万岁！！