openssl学习之ccm，gcm 模式

openssl中添加了对AES ccm 和gcm模式的支持。下面的内容主要是对这两个模式相关资料的收集以及整理。

一，CCM

CCM （counter with CBC-MAC)定义在分组长度为128位的加密算法中，如，AES 的分组长度为128。组成AES-CCM算法的关键组成是CTR工作模式以及CMAC认证算法。Wifi 的WPE协议中使用了AES-CCM。在HMAC中我们介绍CCM是属于一种E&M（认证并且加密），首先我们来看一下AES-CCM模式的输入输出。

首先介绍两个参数设置：

L：长度域，取值为2~8 ，openssl中缺省的为8。

M：tag的长度，合法的值为：4,6,8,10,12,14 和16。openssl中缺省的为12

key	16,24,32
None	15-L
Message to authenticate and encrypt	len(Msg)
Additional authenticated data	len(AAD)

其中对消息长度有：0<= len(Msg)<= 2^(8L);

对附加数据长度有：0<= len(AAD)< 2^64;

[cpp] view plain copy

1. /* Simple AES CCM test program, uses the same NIST data used for the FIPS 
2.  * self test but uses the application level EVP APIs. 
3.  */  
4. #include <stdio.h>  
5. #include <openssl/bio.h>  
6. #include <openssl/evp.h>  
7.   
8. /* AES-CCM test data from NIST public test vectors */  
9.   
10. static const unsigned char ccm_key[] = {  
11.     0xce,0xb0,0x09,0xae,0xa4,0x45,0x44,0x51,0xfe,0xad,0xf0,0xe6,  
12.     0xb3,0x6f,0x45,0x55,0x5d,0xd0,0x47,0x23,0xba,0xa4,0x48,0xe8  
13. };  
14. // 随机数，每次加密针对相同的KEY使用不同的NONCE。否则会破坏CCM模式的安全性（RFC3610）  
15. static const unsigned char ccm_nonce[] = {  
16.     0x76,0x40,0x43,0xc4,0x94,0x60,0xb7  
17. };  
18. //附加数据  
19. static const unsigned char ccm_adata[] = {  
20.     0x6e,0x80,0xdd,0x7f,0x1b,0xad,0xf3,0xa1,0xc9,0xab,0x25,0xc7,  
21.     0x5f,0x10,0xbd,0xe7,0x8c,0x23,0xfa,0x0e,0xb8,0xf9,0xaa,0xa5,  
22.     0x3a,0xde,0xfb,0xf4,0xcb,0xf7,0x8f,0xe4  
23. };  
24. //plaintext 表示明文  
25. static const unsigned char ccm_pt[] = {  
26.     0xc8,0xd2,0x75,0xf9,0x19,0xe1,0x7d,0x7f,0xe6,0x9c,0x2a,0x1f,  
27.     0x58,0x93,0x9d,0xfe,0x4d,0x40,0x37,0x91,0xb5,0xdf,0x13,0x10  
28. };  
29. //ciphertext 表示密文  
30. static const unsigned char ccm_ct[] = {  
31.     0x8a,0x0f,0x3d,0x82,0x29,0xe4,0x8e,0x74,0x87,0xfd,0x95,0xa2,  
32.     0x8a,0xd3,0x92,0xc8,0x0b,0x36,0x81,0xd4,0xfb,0xc7,0xbb,0xfd  
33. };  
34. //tag 表示tag数据  
35. static const unsigned char ccm_tag[] = {  
36.     0x2d,0xd6,0xef,0x1c,0x45,0xd4,0xcc,0xb7,0x23,0xdc,0x07,0x44,  
37.     0x14,0xdb,0x50,0x6d  
38. };  
39.   
40. void aes_ccm_encrypt(void)  
41. {  
42.     EVP_CIPHER_CTX *ctx;  
43.     int outlen, tmplen;  
44.     unsigned char outbuf[1024];  
45.     printf("AES CCM Encrypt:\n");  
46.     printf("Plaintext:\n");  
47.     BIO_dump_fp(stdout, ccm_pt, sizeof(ccm_pt));  
48.     ctx = EVP_CIPHER_CTX_new();  
49.     /* Set cipher type and mode */  
50.     EVP_EncryptInit_ex(ctx, EVP_aes_192_ccm(), NULL, NULL, NULL);  
51.     /* Set nonce length if default 96 bits is not appropriate */  
52.     EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, sizeof(ccm_nonce), NULL);  
53.     /* Set tag length */  
54.     EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, sizeof(ccm_tag), NULL);  
55.     /* Initialise key and IV */  
56.     EVP_EncryptInit_ex(ctx, NULL, NULL, ccm_key, ccm_nonce);  
57.     /* Set plaintext length: only needed if AAD is used*/  
58.         //输入输出需设置为NULL  
59.     EVP_EncryptUpdate(ctx, NULL, &outlen, NULL, sizeof(ccm_pt));  
60.     /* Zero or one call to specify any AAD */  
61.         //设置AAD，out参数需设置为NULL  
62.     EVP_EncryptUpdate(ctx, NULL, &outlen, ccm_adata, sizeof(ccm_adata));  
63.     /* Encrypt plaintext: can only be called once */  
64.     EVP_EncryptUpdate(ctx, outbuf, &outlen, ccm_pt, sizeof(ccm_pt));  
65.     /* Output encrypted block */  
66.     printf("Ciphertext:\n");  
67.     BIO_dump_fp(stdout, outbuf, outlen);  
68.     /* Finalise: note get no output for CCM */  
69.     EVP_EncryptFinal_ex(ctx, outbuf, &outlen);  
70.     /* Get tag */  
71.     EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_GET_TAG, 16, outbuf);  
72.     /* Output tag */  
73.     printf("Tag:\n");  
74.     BIO_dump_fp(stdout, outbuf, 16);  
75.     EVP_CIPHER_CTX_free(ctx);  
76. }  
77.   
78. void aes_ccm_decrypt(void)  
79. {  
80.     EVP_CIPHER_CTX *ctx;  
81.     int outlen, tmplen, rv;  
82.     unsigned char outbuf[1024];  
83.     printf("AES CCM Derypt:\n");  
84.     printf("Ciphertext:\n");  
85.     BIO_dump_fp(stdout, ccm_ct, sizeof(ccm_ct));  
86.     ctx = EVP_CIPHER_CTX_new();  
87.     /* Select cipher */  
88.     EVP_DecryptInit_ex(ctx, EVP_aes_192_ccm(), NULL, NULL, NULL);  
89.     /* Set nonce length, omit for 96 bits */  
90.     EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, sizeof(ccm_nonce), NULL);  
91.     /* Set expected tag value */  
92.     EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG,  
93.                     sizeof(ccm_tag), (void *)ccm_tag);  
94.     /* Specify key and IV */  
95.     EVP_DecryptInit_ex(ctx, NULL, NULL, ccm_key, ccm_nonce);  
96.     /* Set ciphertext length: only needed if we have AAD */  
97.     EVP_DecryptUpdate(ctx, NULL, &outlen, NULL, sizeof(ccm_ct));  
98.     /* Zero or one call to specify any AAD */  
99.     EVP_DecryptUpdate(ctx, NULL, &outlen, ccm_adata, sizeof(ccm_adata));  
100.     /* Decrypt plaintext, verify tag: can only be called once */  
101.     rv = EVP_DecryptUpdate(ctx, outbuf, &outlen, ccm_ct, sizeof(ccm_ct));  
102.     /* Output decrypted block: if tag verify failed we get nothing */  
103.     if (rv > 0)  
104.     {  
105.         printf("Plaintext:\n");  
106.         BIO_dump_fp(stdout, outbuf, outlen);  
107.     }  
108.     else  
109.         printf("Plaintext not available: tag verify failed.\n");  
110.     EVP_CIPHER_CTX_free(ctx);  
111. }  
112.   
113. int main(int argc, char **argv)  
114. {  
115.     aes_ccm_encrypt();  
116.     aes_ccm_decrypt();  
117. }  

2，GCM 

GCM基于并行化设计，因此可以提供高效的吞吐率和低成本、低时延。本质是消息在变形的CTR模式下加密，密文结果与密钥以及消息长度在GF（2^128）域上相乘，计算流程如下所示。其输入输出和CCM基本一致。CCM和GCM的具体计算过程可以参看《密码学与网络安全》第五版，书中有详细的介绍。FRC5288 中介绍了TLS1.2 中的GCM应用。下面贴出openssl中AES-GCM的实例。

[cpp] view plain copy

1. /* Simple AES GCM test program, uses the same NIST data used for the FIPS 
2.  * self test but uses the application level EVP APIs. 
3.  */  
4. #include <stdio.h>  
5. #include <openssl/bio.h>  
6. #include <openssl/evp.h>  
7.   
8. /* AES-GCM test data from NIST public test vectors */  
9.   
10. static const unsigned char gcm_key[] = {  
11.         0xee,0xbc,0x1f,0x57,0x48,0x7f,0x51,0x92,0x1c,0x04,0x65,0x66,  
12.         0x5f,0x8a,0xe6,0xd1,0x65,0x8b,0xb2,0x6d,0xe6,0xf8,0xa0,0x69,  
13.         0xa3,0x52,0x02,0x93,0xa5,0x72,0x07,0x8f  
14. };  
15.   
16. static const unsigned char gcm_iv[] = {  
17.         0x99,0xaa,0x3e,0x68,0xed,0x81,0x73,0xa0,0xee,0xd0,0x66,0x84  
18. };  
19.   
20. static const unsigned char gcm_pt[] = {  
21.         0xf5,0x6e,0x87,0x05,0x5b,0xc3,0x2d,0x0e,0xeb,0x31,0xb2,0xea,  
22.         0xcc,0x2b,0xf2,0xa5  
23. };  
24.   
25. static const unsigned char gcm_aad[] = {  
26.         0x4d,0x23,0xc3,0xce,0xc3,0x34,0xb4,0x9b,0xdb,0x37,0x0c,0x43,  
27.         0x7f,0xec,0x78,0xde  
28. };  
29.   
30. static const unsigned char gcm_ct[] = {  
31.         0xf7,0x26,0x44,0x13,0xa8,0x4c,0x0e,0x7c,0xd5,0x36,0x86,0x7e,  
32.         0xb9,0xf2,0x17,0x36  
33. };  
34.   
35. static const unsigned char gcm_tag[] = {  
36.         0x67,0xba,0x05,0x10,0x26,0x2a,0xe4,0x87,0xd7,0x37,0xee,0x62,  
37.         0x98,0xf7,0x7e,0x0c  
38. };  
39.   
40. void aes_gcm_encrypt(void)  
41. {  
42.         EVP_CIPHER_CTX *ctx;  
43.         int outlen, tmplen;  
44.         unsigned char outbuf[1024];  
45.         printf("AES GCM Encrypt:\n");  
46.         printf("Plaintext:\n");  
47.         BIO_dump_fp(stdout, gcm_pt, sizeof(gcm_pt));  
48.         ctx = EVP_CIPHER_CTX_new();  
49.         /* Set cipher type and mode */  
50.         EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);  
51.         /* Set IV length if default 96 bits is not appropriate */  
52.         EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);  
53.         /* Initialise key and IV */  
54.         EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);  
55.         /* Zero or more calls to specify any AAD */  
56.         EVP_EncryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));  
57.         /* Encrypt plaintext */  
58.         EVP_EncryptUpdate(ctx, outbuf, &outlen, gcm_pt, sizeof(gcm_pt));  
59.         /* Output encrypted block */  
60.         printf("Ciphertext:\n");  
61.         BIO_dump_fp(stdout, outbuf, outlen);  
62.         /* Finalise: note get no output for GCM */  
63.         EVP_EncryptFinal_ex(ctx, outbuf, &outlen);  
64.         /* Get tag */  
65.         EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, outbuf);  
66.         /* Output tag */  
67.         printf("Tag:\n");  
68.         BIO_dump_fp(stdout, outbuf, 16);  
69.         EVP_CIPHER_CTX_free(ctx);  
70. }  
71.   
72. void aes_gcm_decrypt(void)  
73. {  
74.         EVP_CIPHER_CTX *ctx;  
75.         int outlen, tmplen, rv;  
76.         unsigned char outbuf[1024];  
77.         printf("AES GCM Derypt:\n");  
78.         printf("Ciphertext:\n");  
79.         BIO_dump_fp(stdout, gcm_ct, sizeof(gcm_ct));  
80.         ctx = EVP_CIPHER_CTX_new();  
81.         /* Select cipher */  
82.         EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);  
83.         /* Set IV length, omit for 96 bits */  
84.         EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);  
85.         /* Specify key and IV */  
86.         EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);  
87. #if 0  
88.         /* Set expected tag value. A restriction in OpenSSL 1.0.1c and earlier 
89.          * required the tag before any AAD or ciphertext */  
90.         EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);  
91. #endif  
92.         /* Zero or more calls to specify any AAD */  
93.         EVP_DecryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));  
94.         /* Decrypt plaintext */  
95.         EVP_DecryptUpdate(ctx, outbuf, &outlen, gcm_ct, sizeof(gcm_ct));  
96.         /* Output decrypted block */  
97.         printf("Plaintext:\n");  
98.         BIO_dump_fp(stdout, outbuf, outlen);  
99.         /* Set expected tag value. Works in OpenSSL 1.0.1d and later */  
100.         EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);  
101.         /* Finalise: note get no output for GCM */  
102.         rv = EVP_DecryptFinal_ex(ctx, outbuf, &outlen);  
103.         /* Print out return value. If this is not successful authentication 
104.          * failed and plaintext is not trustworthy. 
105.          */  
106.         printf("Tag Verify %s\n", rv > 0 ? "Successful!" : "Failed!");  
107.         EVP_CIPHER_CTX_free(ctx);  
108.  }  
109.   
110. int main(int argc, char **argv)  
111. {  
112.         aes_gcm_encrypt();  
113.         aes_gcm_decrypt();  
114.  }