关于各种加密方式的使用场景##
1.通过简单的URLENCODE ＋ BASE64编码防止数据明文传输
2.对普通请求、返回数据，生成MD5校验（MD5中加入动态密钥），进行数据完整性（简单防篡改，安全性较低，优点：快速）校验。
3.对于重要数据，使用RSA进行数字签名，起到防篡改作用。
4.对于比较敏感的数据，如用户信息（登陆、注册等），客户端发送使用RSA加密，服务器返回使用DES(AES)加密。
注：客户端发送之所以使用RSA加密，是因为RSA解密需要知道服务器私钥，而服务器私钥一般盗取难度较大；如果使用DES的话，可以通过破解客户端获取密钥，安全性较低。而服务器返回之所以使用DES，是因为不管使用DES还是RSA，密钥（或私钥）都存储在客户端，都存在被破解的风险，而RSA速度比较慢，所以使用DES。
1.DM5###
//因为是使用category，没有参数传入
-(NSString *) stringFromMD5 {
if(self == nil || [self length] == 0) {
return nil;
}
const char *value = [self UTF8String];
unsigned char outputBuffer[CC_MD5_DIGEST_LENGTH];
CC_MD5(value, strlen(value), outputBuffer);
NSMutableString *outputString = [[NSMutableString alloc] initWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
for(NSInteger count = 0; count < CC_MD5_DIGEST_LENGTH; count++){
[outputString appendFormat:@"%02x",outputBuffer[count]];
}
return [outputString autorelease];
}
2.Base64###
+ (NSString *) base64EncodeData: (NSData *) objData {
const unsigned char * objRawData = [objData bytes];
char * objPointer;char * strResult;
// Get the Raw Data length and ensure we actually have data
int intLength = [objData length];
if (intLength == 0) return nil;
// Setup the String-based Result placeholder and pointer within that placeholder
strResult = (char *)calloc(((intLength + 2) / 3) * 4, sizeof(char));
objPointer = strResult;
// Iterate through everything
while (intLength > 2) {
// keep going until we have less than 24 bits*objPointer++ = _base64EncodingTable[objRawData[0] >> 2];
*objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
*objPointer++ = _base64EncodingTable[((objRawData[1] & 0x0f) << 2) + (objRawData[2] >> 6)];
*objPointer++ = _base64EncodingTable[objRawData[2] & 0x3f];
// we just handled 3 octets (24 bits) of data
objRawData += 3;
intLength -= 3;
}
// now deal with the tail end of things
if (intLength != 0) {
*objPointer++ = _base64EncodingTable[objRawData[0] >> 2];
if (intLength > 1) {
*objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
*objPointer++ = _base64EncodingTable[(objRawData[1] & 0x0f) << 2];
*objPointer++ = '=';
}
else {
*objPointer++ = _base64EncodingTable[(objRawData[0] & 0x03) << 4];
*objPointer++ = '=';
*objPointer++ = '=';
}
}// Terminate the string-based result
*objPointer = '\0';
NSString *rstStr = [NSString stringWithCString:strResult encoding:NSASCIIStringEncoding];
free(objPointer);
return rstStr;
}
3.AES###
-(NSData*) EncryptAES: (NSString *) key {
char keyPtr[kCCKeySizeAES256+1];
bzero(keyPtr, sizeof(keyPtr));
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,kCCOptionPKCS7Padding | kCCOptionECBMode,keyPtr, kCCBlockSizeAES128,NULL,[self bytes], dataLength,buffer, bufferSize,&numBytesEncrypted);
if (cryptStatus == kCCSuccess) {
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
free(buffer);
return nil;
}
4.RSA###
- (NSData *) encryptWithData:(NSData *)content {
size_t plainLen = [content length];if (plainLen > maxPlainLen) {
NSLog(@"content(%ld) is too long, must < %ld", plainLen, maxPlainLen);
return nil;
}
void *plain = malloc(plainLen);
[content getBytes:plainlength:plainLen];
size_t cipherLen = 128; // currently RSA key length is set to 128 bytes
void *cipher = malloc(cipherLen);
OSStatus returnCode = SecKeyEncrypt(publicKey, kSecPaddingPKCS1, plain,plainLen, cipher, &cipherLen);
NSData *result = nil;
if (returnCode != 0) {
NSLog(@"SecKeyEncrypt fail. Error Code: %ld", returnCode);
}
else {
result = [NSData dataWithBytes:cipherlength:cipherLen];
}
free(plain);
free(cipher);
return result;
}