add HMAC-MD5 implementation

2 files changed, 76 insertions, 0 deletions

diff --git a/src/md5.c b/src/md5.c
index bb4546e..30cad65 100644
--- a/src/md5.c
+++ b/src/md5.c
@@ -173,6 +173,79 @@ void MD5Final(unsigned char digest[16], struct MD5Context *ctx)
 	memset(ctx, 0, sizeof(*ctx));	/* In case it's sensitive */
 }
 
+/** Calculate HMAC using internal MD5 implementation
+ *
+ * @param digest Caller digest to be filled in.
+ * @param text Pointer to data stream.
+ * @param text_len length of data stream.
+ * @param key Pointer to authentication key.
+ * @param key_len Length of authentication key.
+ *
+ */
+void hmac_md5(uint8_t digest[16], uint8_t const *text, size_t text_len,
+		 uint8_t const *key, size_t key_len)
+{
+	MD5_CTX context;
+	uint8_t k_ipad[65];    /* inner padding - key XORd with ipad */
+	uint8_t k_opad[65];    /* outer padding - key XORd with opad */
+	uint8_t tk[16];
+	int i;
+
+	/* if key is longer than 64 bytes reset it to key=MD5(key) */
+	if (key_len > 64) {
+		MD5_CTX tctx;
+
+		MD5Init(&tctx);
+		MD5Update(&tctx, key, key_len);
+		MD5Final(tk, &tctx);
+
+		key = tk;
+		key_len = 16;
+	}
+
+	/*
+	 * the HMAC_MD5 transform looks like:
+	 *
+	 * MD5(K XOR opad, MD5(K XOR ipad, text))
+	 *
+	 * where K is an n byte key
+	 * ipad is the byte 0x36 repeated 64 times
+
+	 * opad is the byte 0x5c repeated 64 times
+	 * and text is the data being protected
+	 */
+
+	/* start out by storing key in pads */
+	memset( k_ipad, 0, sizeof(k_ipad));
+	memset( k_opad, 0, sizeof(k_opad));
+	memcpy( k_ipad, key, key_len);
+	memcpy( k_opad, key, key_len);
+
+	/* XOR key with ipad and opad values */
+	for (i = 0; i < 64; i++) {
+		k_ipad[i] ^= 0x36;
+		k_opad[i] ^= 0x5c;
+	}
+	/*
+	 * perform inner MD5
+	 */
+	MD5Init(&context);		   /* init context for 1st
+					      * pass */
+	MD5Update(&context, k_ipad, 64);      /* start with inner pad */
+	MD5Update(&context, text, text_len); /* then text of datagram */
+	MD5Final(digest, &context);	  /* finish up 1st pass */
+	/*
+	 * perform outer MD5
+	 */
+	MD5Init(&context);		   /* init context for 2nd
+					      * pass */
+	MD5Update(&context, k_opad, 64);     /* start with outer pad */
+	MD5Update(&context, digest, 16);     /* then results of 1st
+					      * hash */
+	MD5Final(digest, &context);	  /* finish up 2nd pass */
+}
+
+
 #ifndef ASM_MD5
 
 /* The four core functions - F1 is optimized somewhat */
diff --git a/src/md5.h b/src/md5.h
index ce0e350..90c571b 100644
--- a/src/md5.h
+++ b/src/md5.h
@@ -51,6 +51,9 @@ void MD5Update(struct MD5Context *, unsigned const char *, unsigned);
 void MD5Final(unsigned char digest[16], struct MD5Context *);
 void MD5Transform(uint32_t buf[4], uint32_t const in[16]);
 
+void hmac_md5(uint8_t digest[16], uint8_t const *text, size_t text_len,
+	      uint8_t const *key, size_t key_len);
+
 /*
  * This is needed to make RSAREF happy on some MS-DOS compilers.
  */