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hmac.c

/***************************************************************************
* From Appendix B of:                                                      *
* Network Working Group                                          C. Newman *
* Internet Draft: SCRAM-MD5 SASL Mechanism                        Innosoft *
* Document: draft-newman-auth-scram-02.txt                    January 1998 *
*                                                    Expires in six months *
***************************************************************************/

/* hmac-md5.c -- HMAC MD5 Keyed-Hashing by Chris Newman
 *  derived from RFC 2104 by H. Krawczyk, M. Bellare, R.Canetti
 */

#include <stdio.h>
#include <string.h>
#include "md5.h"
#include "hmac-md5.h"


/* for htonl() and ntohl() */

#include <sys/types.h>
#include <netinet/in.h>


/* MD5 block size */

#define BLOCK_SIZE 64

void hmac_md5_init(HMAC_MD5_CTX *hmac,
        const unsigned char *key, int key_len)
{
    unsigned char k_pad[BLOCK_SIZE];    /* padded key */
    int i;

    /* if key longer than BLOCK_SIZE bytes reset to MD5(key) */
    if (key_len > BLOCK_SIZE) {
     MD5Init(&hmac->ictx);
     MD5Update(&hmac->ictx, key, key_len);
     MD5Final(k_pad, &hmac->ictx);
     key = k_pad;
     key_len = HMAC_MD5_SIZE;
    }

    /* XOR padded key with inner pad value */

    for (i = 0; i < key_len; i++) {
     k_pad[i] = key[i] ^ 0x36;
    }
    while (i < BLOCK_SIZE) {
     k_pad[i++] = 0x36;
    }

    /* Begin inner MD5 */

    MD5Init(&hmac->ictx);
    MD5Update(&hmac->ictx, k_pad, BLOCK_SIZE);

    /* XOR padded key with outer pad value */

    for (i = 0; i < BLOCK_SIZE; ++i) {
     k_pad[i] ^= (0x36 ^ 0x5c);
    }

    /* Begin outer MD5 */

    MD5Init(&hmac->octx);
    MD5Update(&hmac->octx, k_pad, BLOCK_SIZE);

    /* clean up workspace */

    memset(k_pad, 0, BLOCK_SIZE);
}


void hmac_md5_final(unsigned char digest[HMAC_MD5_SIZE],
         HMAC_MD5_CTX *hmac)
{
    /* finish inner MD5 */
    MD5Final(digest, &hmac->ictx);
    /* finish outer MD5 */
    MD5Update(&hmac->octx, digest, HMAC_MD5_SIZE);
    MD5Final(digest, &hmac->octx);
    /* MD5Final zeros context */
}


void hmac_md5(const unsigned char *text, int text_len,
           const unsigned char *key, int key_len,
           unsigned char digest[HMAC_MD5_SIZE])
{
    HMAC_MD5_CTX hmac;

    hmac_md5_init(&hmac, key, key_len);
    hmac_md5_update(&hmac, text, text_len);
    hmac_md5_final(digest, &hmac);
}


void hmac_md5_precalc(HMAC_MD5_STATE *ctx,
     const unsigned char *pass, int passlen)
{
    HMAC_MD5_CTX hctx;

    if (passlen == 0) passlen = strlen((const char *) pass);
    hmac_md5_init(&hctx, pass, passlen);
    ctx->istate[0] = htonl(hctx.ictx.state[0]);
    ctx->istate[1] = htonl(hctx.ictx.state[1]);
    ctx->istate[2] = htonl(hctx.ictx.state[2]);
    ctx->istate[3] = htonl(hctx.ictx.state[3]);
    ctx->ostate[0] = htonl(hctx.octx.state[0]);
    ctx->ostate[1] = htonl(hctx.octx.state[1]);
    ctx->ostate[2] = htonl(hctx.octx.state[2]);
    ctx->ostate[3] = htonl(hctx.octx.state[3]);
    memset(&hctx, 0, sizeof (hctx));
}


void hmac_md5_import(HMAC_MD5_CTX *hctx, HMAC_MD5_STATE *ctx)
{
    hctx->ictx.state[0] = ntohl(ctx->istate[0]);
    hctx->ictx.state[1] = ntohl(ctx->istate[1]);
    hctx->ictx.state[2] = ntohl(ctx->istate[2]);
    hctx->ictx.state[3] = ntohl(ctx->istate[3]);
    hctx->octx.state[0] = ntohl(ctx->ostate[0]);
    hctx->octx.state[1] = ntohl(ctx->ostate[1]);
    hctx->octx.state[2] = ntohl(ctx->ostate[2]);
    hctx->octx.state[3] = ntohl(ctx->ostate[3]);
    hctx->ictx.count[0] = hctx->octx.count[0] = BLOCK_SIZE << 3;
    hctx->ictx.count[1] = hctx->octx.count[1] = 0;
}


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