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1 /*
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2 ** Function: hmac_md5
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3 */
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4
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5 #include <string.h>
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6 #include "md5.h"
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7 #include "hmac_md5.h"
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8
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9 void
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10 hmac_md5(unsigned char *text, int text_len, unsigned char *key, int key_len, unsigned char *digest)
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11 /* text; pointer to data stream */
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12 /* text_len; length of data stream */
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13 /* key; pointer to authentication key */
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14 /* key_len; length of authentication key */
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15 /* digest; caller digest to be filled in */
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16 {
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17 MD5_CTX context;
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18 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */
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19 unsigned char k_opad[65]; /* outer padding - key XORd with opad */
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20 unsigned char tk[16];
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21 int i;
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22 /* if key is longer than 64 bytes reset it to key=MD5(key) */
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23 if (key_len > 64) {
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24
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25 MD5_CTX tctx;
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26
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27 MD5_Init(&tctx);
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28 MD5_Update(&tctx, key, key_len);
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29 MD5_Final(tk, &tctx);
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30
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31 key = tk;
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32 key_len = 16;
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33 }
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34
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35 /*
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36 * the HMAC_MD5 transform looks like:
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37 *
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38 * MD5(K XOR opad, MD5(K XOR ipad, text))
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39 *
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40 * where K is an n byte key
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41 * ipad is the byte 0x36 repeated 64 times
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42 * opad is the byte 0x5c repeated 64 times
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43 * and text is the data being protected
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44 */
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45
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46 /* start out by storing key in pads */
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47 bzero(k_ipad, sizeof k_ipad);
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48 bzero(k_opad, sizeof k_opad);
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49 bcopy(key, k_ipad, key_len);
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50 bcopy(key, k_opad, key_len);
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51
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52 /* XOR key with ipad and opad values */
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53 for (i = 0; i < 64; i++) {
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54 k_ipad[i] ^= 0x36;
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55 k_opad[i] ^= 0x5c;
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56 }
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57 /*
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58 * perform inner MD5
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59 */
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60 MD5_Init(&context); /* init context for 1st pass */
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61 MD5_Update(&context, k_ipad, 64); /* start with inner pad */
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62 MD5_Update(&context, text, text_len); /* then text of datagram */
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63 MD5_Final(digest, &context); /* finish up 1st pass */
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64 /*
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65 * perform outer MD5
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66 */
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67 MD5_Init(&context); /* init context for 2nd pass */
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68 MD5_Update(&context, k_opad, 64); /* start with outer pad */
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69 MD5_Update(&context, digest, 16); /* then results of 1st hash */
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70 MD5_Final(digest, &context); /* finish up 2nd pass */
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71 }
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