Linux内核的加密函数框架

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Linux内核支持很多加密算法，包括对称加密算法，如AES；摘要算法，如sha1,md5；压缩算法，如deflate。不过内核好像不支持非对称加密算法。这些算法作为加密函数框架的最底层，提供加密和解密的实际操作。这些函数可以在内核crypto文件夹下，相应的文件中找到。不过内核模块不能直接调用这些函数，因为它们并没有export。内核提供一个统一的框架，来管理这些算法。加密算法通过crypto_register_alg()和crypto_unregister_alg()注册。内核将加密算法分为三类，1）cipher，2）compress，3）digest。加密函数框架中有相应的API封装，提供给模块调用。

对于使用这些加密函数，首先通过crypto_alloc_tfm()来分配一个加密函数对象的实例。初始化这些实例，然后就可以通过框架提供的API对数据进行加密和解密。完成以后，必须通过crypto_free_tfm()撤销实例。

下面是几个代码，或许能够够对内核的加密框架有更直观的了解：

1）digest算法（sha1）

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

struct crypto_tfm *tfm;
struct scatterlist sg[1];
char * code1 = "2ew34123132513451345";
char * code2 = "234123132513451345";

char *do_digest(char * code) {
    char *result;
    int code_len = strlen(code);
    
        tfm = crypto_alloc_tfm("sha1",0);
        if(IS_ERR(tfm))
                return 0;
        sg_init_one(sg,code,code_len);

        crypto_digest_init(tfm);
        crypto_digest_update(tfm,sg,1);
    result = (char *)kmalloc(sizeof(char)*50,GFP_KERNEL);
    if(result == NULL) {
        crypto_free_tfm(tfm);
        return 0;
    }
    memset(result,0,sizeof(char)*50);
    crypto_digest_final(tfm,result);
        crypto_free_tfm(tfm);
    return result;
} 

static int __init test_init(void)
{
    char *result1,*result2;
    result1 = do_digest(code1);
    if(!result1)
        goto failed2;
    result2 = do_digest(code2);
    if(!result2)
        goto failed1;
    
    if(memcmp(result1,result2,50) != 0)
        printk("<1>code1 != code2\n");
    else
        printk("<1>code1 == code2\n");
    kfree(result2);
failed1:
    kfree(result1);
failed2:
    return 0;
}

static void __exit test_exit(void)
{

}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("richardhesidu@chinaunix");

2)compress算法（deflate）

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

struct crypto_tfm *tfm;
char * code = "Hello everyone, I'm richardhesidu from chinaunix.net !";


static inline  void hexdump(unsigned char *buf,unsigned int len) {
    while(len--)
        printk("0x%02x,",*buf++);
    printk("\n");
}

static int __init test_init(void) {
    int ret,result_len,temp_len;
    char result[512];
    char temp[512];

    printk("<1>%s\n",code);    
    
    /* Allocate transform for deflate */
            
    tfm = crypto_alloc_tfm("deflate",0);
        if(IS_ERR(tfm)) {
        printk("<1>failed to load transform for deflate !\n");
                return 0;
    }

    memset(result,0,sizeof(result));

    temp_len = 512;
    ret = crypto_comp_compress(tfm,code,strlen(code),temp,&temp_len);
    if(ret) {
        printk("<1>failed to compress !\n");
        return 0;
    }
      
    hexdump(temp,strlen(temp));
    
    memset(result,0,sizeof(result));

    result_len = 512;
    ret = crypto_comp_decompress(tfm,temp,strlen(temp),result,&result_len);
    if(ret) {
                printk("<1>failed to decompress !\n");
                return 0;
        }

    printk("<1>%s\n",result);

    if(memcmp(code,result,strlen(code)) != 0)
        printk("<1>decompressed was not successful\n");
    else
        printk("<1>decompressed was successful\n");

           crypto_free_tfm(tfm);
    return 0;
}

static void __exit test_exit(void)
{

}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("richardhesidu@chinaunix");

3)cipher算法（aes）

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

struct crypto_tfm *tfm;
#if 1
char *code = "Hello everyone,I'm Richardhesidu"
        "Hello everyone,I'm Richardhesidu"
            "Hello everyone,I'm Richardhesidu";

char *key = "00112233445566778899aabbccddeeff";
#endif

#if 0
char code[] = {0x00,0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xaa,
        0xbb,0xcc,0xdd,0xee,0xff};
char key[] = {0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0a,
        0x0b,0x0c,0x0d,0x0e,0x0f};
#endif

static inline  void hexdump(unsigned char *buf,unsigned int len) {
    while(len--)
        printk("%02x",*buf++);
    printk("\n");
}

static int __init test_init(void) {
    int ret,templen,keylen,codelen;
    struct scatterlist sg[1];
    char *result;
    char *temp;

    keylen = 16;
    codelen = strlen(code)/2;
#if 0
    printk("<1>%s, codelen=%d\n",code,strlen(code));
    printk("<1>%s, keylen=%d\n",key,strlen(key));    
#endif    
    /* Allocate transform for AES ECB mode */
            
    tfm = crypto_alloc_tfm("aes",CRYPTO_TFM_MODE_ECB);
        if(IS_ERR(tfm)) {
        printk("<1>failed to load transform for aes ECB mode !\n");
                return 0;
    }

    ret = crypto_cipher_setkey(tfm,key,keylen);
    if(ret) {
        printk("<1>failed to setkey \n");
        goto failed1;
    } 
    
    sg_init_one(sg,code,codelen);
        
    /* start encrypt */
    
    ret = crypto_cipher_encrypt(tfm,sg,sg,codelen);
    if(ret) {
        printk("<1>encrypt failed \n");
        goto failed1;
    }
    
    temp = kmap(sg[0].page) + sg[0].offset;

    hexdump(temp,sg[0].length);
    
          /* start dencrypt */
    templen = strlen(temp)/2;
    sg_init_one(sg,temp,templen);
    ret = crypto_cipher_decrypt(tfm,sg,sg,templen);
        if(ret) {
                printk("<1>dencrypt failed \n");
                goto failed1;
        }

        result = kmap(sg[0].page) + sg[0].offset;
    printk("<1>%s\n",result);
//        hexdump(result,sg[0].length);


#if 0
    if(memcmp(code,result,strlen(code)) != 0)
        printk("<1>dencrpt was not successful\n");
    else
        printk("<1>dencrypt was successful\n");
#endif
failed1:
           crypto_free_tfm(tfm);
    return 0;
}

static void __exit test_exit(void)
{

}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("richardhesidu@chinaunix");