1 /*

2 ** Function: hmac_md5

3 */

4

5 #include <string.h>

6 #include "global.h"

7 #include "md5.h"

8 #include "hmac_md5.h"

9

10 void

11 hmac_md5(unsigned char *text, int text_len, unsigned char *key, int key_len, unsigned char *digest)

12 /* text; pointer to data stream */

13 /* text_len; length of data stream */

14 /* key; pointer to authentication key */

15 /* key_len; length of authentication key */

16 /* digest; caller digest to be filled in */

17 {

18 MD5_CTX context;

19 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */

20 unsigned char k_opad[65]; /* outer padding - key XORd with opad */

21 unsigned char tk[16];

22 int i;

23 /* if key is longer than 64 bytes reset it to key=MD5(key) */

24 if (key_len > 64) {

25

26 MD5_CTX tctx;

27

28 MD5Init(&tctx);

29 MD5Update(&tctx, key, key_len);

30 MD5Final(tk, &tctx);

31

32 key = tk;

33 key_len = 16;

34 }

35

36 /*

37 * the HMAC_MD5 transform looks like:

38 *

39 * MD5(K XOR opad, MD5(K XOR ipad, text))

40 *

41 * where K is an n byte key

42 * ipad is the byte 0x36 repeated 64 times

43 * opad is the byte 0x5c repeated 64 times

44 * and text is the data being protected

45 */

46

47 /* start out by storing key in pads */

48 bzero(k_ipad, sizeof k_ipad);

49 bzero(k_opad, sizeof k_opad);

50 bcopy(key, k_ipad, key_len);

51 bcopy(key, k_opad, key_len);

52

53 /* XOR key with ipad and opad values */

54 for (i = 0; i < 64; i++) {

55 k_ipad[i] ^= 0x36;

56 k_opad[i] ^= 0x5c;

57 }

58 /*

59 * perform inner MD5

60 */

61 MD5Init(&context); /* init context for 1st pass */

62 MD5Update(&context, k_ipad, 64); /* start with inner pad */

63 MD5Update(&context, text, text_len); /* then text of datagram */

64 MD5Final(digest, &context); /* finish up 1st pass */

65 /*

66 * perform outer MD5

67 */

68 MD5Init(&context); /* init context for 2nd pass */

69 MD5Update(&context, k_opad, 64); /* start with outer pad */

70 MD5Update(&context, digest, 16); /* then results of 1st hash */

71 MD5Final(digest, &context); /* finish up 2nd pass */

72 }