Refactor HMAC implementations

Similarly to the cryptohash implementations, this refactors the existing
HMAC code into a single set of APIs that can be plugged with any crypto
libraries PostgreSQL is built with (only OpenSSL currently).  If there
is no such libraries, a fallback implementation is available.  Those new
APIs are designed similarly to the existing cryptohash layer, so there
is no real new design here, with the same logic around buffer bound
checks and memory handling.

HMAC has a dependency on cryptohashes, so all the cryptohash types
supported by cryptohash{_openssl}.c can be used with HMAC.  This
refactoring is an advantage mainly for SCRAM, that included its own
implementation of HMAC with SHA256 without relying on the existing
crypto libraries even if PostgreSQL was built with their support.

This code has been tested on Windows and Linux, with and without
OpenSSL, across all the versions supported on HEAD from 1.1.1 down to
1.0.1.  I have also checked that the implementations are working fine
using some sample results, a custom extension of my own, and doing
cross-checks across different major versions with SCRAM with the client
and the backend.

Author: Michael Paquier
Reviewed-by: Bruce Momjian
Discussion: https://postgr.es/m/X9m0nkEJEzIPXjeZ@paquier.xyz

1 files changed, 33 insertions, 125 deletions

diff --git a/src/common/scram-common.c b/src/common/scram-common.c
index 0b9557376e9..69a96f65f65 100644
--- a/src/common/scram-common.c
+++ b/src/common/scram-common.c
@@ -20,118 +20,10 @@
 #endif
 
 #include "common/base64.h"
+#include "common/hmac.h"
 #include "common/scram-common.h"
 #include "port/pg_bswap.h"
 
-#define HMAC_IPAD 0x36
-#define HMAC_OPAD 0x5C
-
-/*
- * Calculate HMAC per RFC2104.
- *
- * The hash function used is SHA-256.  Returns 0 on success, -1 on failure.
- */
-int
-scram_HMAC_init(scram_HMAC_ctx *ctx, const uint8 *key, int keylen)
-{
-	uint8		k_ipad[SHA256_HMAC_B];
-	int			i;
-	uint8		keybuf[SCRAM_KEY_LEN];
-
-	/*
-	 * If the key is longer than the block size (64 bytes for SHA-256), pass
-	 * it through SHA-256 once to shrink it down.
-	 */
-	if (keylen > SHA256_HMAC_B)
-	{
-		pg_cryptohash_ctx *sha256_ctx;
-
-		sha256_ctx = pg_cryptohash_create(PG_SHA256);
-		if (sha256_ctx == NULL)
-			return -1;
-		if (pg_cryptohash_init(sha256_ctx) < 0 ||
-			pg_cryptohash_update(sha256_ctx, key, keylen) < 0 ||
-			pg_cryptohash_final(sha256_ctx, keybuf, sizeof(keybuf)) < 0)
-		{
-			pg_cryptohash_free(sha256_ctx);
-			return -1;
-		}
-		key = keybuf;
-		keylen = SCRAM_KEY_LEN;
-		pg_cryptohash_free(sha256_ctx);
-	}
-
-	memset(k_ipad, HMAC_IPAD, SHA256_HMAC_B);
-	memset(ctx->k_opad, HMAC_OPAD, SHA256_HMAC_B);
-
-	for (i = 0; i < keylen; i++)
-	{
-		k_ipad[i] ^= key[i];
-		ctx->k_opad[i] ^= key[i];
-	}
-
-	ctx->sha256ctx = pg_cryptohash_create(PG_SHA256);
-	if (ctx->sha256ctx == NULL)
-		return -1;
-
-	/* tmp = H(K XOR ipad, text) */
-	if (pg_cryptohash_init(ctx->sha256ctx) < 0 ||
-		pg_cryptohash_update(ctx->sha256ctx, k_ipad, SHA256_HMAC_B) < 0)
-	{
-		pg_cryptohash_free(ctx->sha256ctx);
-		return -1;
-	}
-
-	return 0;
-}
-
-/*
- * Update HMAC calculation
- * The hash function used is SHA-256.  Returns 0 on success, -1 on failure.
- */
-int
-scram_HMAC_update(scram_HMAC_ctx *ctx, const char *str, int slen)
-{
-	Assert(ctx->sha256ctx != NULL);
-	if (pg_cryptohash_update(ctx->sha256ctx, (const uint8 *) str, slen) < 0)
-	{
-		pg_cryptohash_free(ctx->sha256ctx);
-		return -1;
-	}
-	return 0;
-}
-
-/*
- * Finalize HMAC calculation.
- * The hash function used is SHA-256.  Returns 0 on success, -1 on failure.
- */
-int
-scram_HMAC_final(uint8 *result, scram_HMAC_ctx *ctx)
-{
-	uint8		h[SCRAM_KEY_LEN];
-
-	Assert(ctx->sha256ctx != NULL);
-
-	if (pg_cryptohash_final(ctx->sha256ctx, h, sizeof(h)) < 0)
-	{
-		pg_cryptohash_free(ctx->sha256ctx);
-		return -1;
-	}
-
-	/* H(K XOR opad, tmp) */
-	if (pg_cryptohash_init(ctx->sha256ctx) < 0 ||
-		pg_cryptohash_update(ctx->sha256ctx, ctx->k_opad, SHA256_HMAC_B) < 0 ||
-		pg_cryptohash_update(ctx->sha256ctx, h, SCRAM_KEY_LEN) < 0 ||
-		pg_cryptohash_final(ctx->sha256ctx, result, SCRAM_KEY_LEN) < 0)
-	{
-		pg_cryptohash_free(ctx->sha256ctx);
-		return -1;
-	}
-
-	pg_cryptohash_free(ctx->sha256ctx);
-	return 0;
-}
-
 /*
  * Calculate SaltedPassword.
  *
@@ -149,7 +41,10 @@ scram_SaltedPassword(const char *password,
 				j;
 	uint8		Ui[SCRAM_KEY_LEN];
 	uint8		Ui_prev[SCRAM_KEY_LEN];
-	scram_HMAC_ctx hmac_ctx;
+	pg_hmac_ctx *hmac_ctx = pg_hmac_create(PG_SHA256);
+
+	if (hmac_ctx == NULL)
+		return -1;
 
 	/*
 	 * Iterate hash calculation of HMAC entry using given salt.  This is
@@ -158,11 +53,12 @@ scram_SaltedPassword(const char *password,
 	 */
 
 	/* First iteration */
-	if (scram_HMAC_init(&hmac_ctx, (uint8 *) password, password_len) < 0 ||
-		scram_HMAC_update(&hmac_ctx, salt, saltlen) < 0 ||
-		scram_HMAC_update(&hmac_ctx, (char *) &one, sizeof(uint32)) < 0 ||
-		scram_HMAC_final(Ui_prev, &hmac_ctx) < 0)
+	if (pg_hmac_init(hmac_ctx, (uint8 *) password, password_len) < 0 ||
+		pg_hmac_update(hmac_ctx, (uint8 *) salt, saltlen) < 0 ||
+		pg_hmac_update(hmac_ctx, (uint8 *) &one, sizeof(uint32)) < 0 ||
+		pg_hmac_final(hmac_ctx, Ui_prev, sizeof(Ui_prev)) < 0)
 	{
+		pg_hmac_free(hmac_ctx);
 		return -1;
 	}
 
@@ -171,10 +67,11 @@ scram_SaltedPassword(const char *password,
 	/* Subsequent iterations */
 	for (i = 2; i <= iterations; i++)
 	{
-		if (scram_HMAC_init(&hmac_ctx, (uint8 *) password, password_len) < 0 ||
-			scram_HMAC_update(&hmac_ctx, (const char *) Ui_prev, SCRAM_KEY_LEN) < 0 ||
-			scram_HMAC_final(Ui, &hmac_ctx) < 0)
+		if (pg_hmac_init(hmac_ctx, (uint8 *) password, password_len) < 0 ||
+			pg_hmac_update(hmac_ctx, (uint8 *) Ui_prev, SCRAM_KEY_LEN) < 0 ||
+			pg_hmac_final(hmac_ctx, Ui, sizeof(Ui)) < 0)
 		{
+			pg_hmac_free(hmac_ctx);
 			return -1;
 		}
 
@@ -183,6 +80,7 @@ scram_SaltedPassword(const char *password,
 		memcpy(Ui_prev, Ui, SCRAM_KEY_LEN);
 	}
 
+	pg_hmac_free(hmac_ctx);
 	return 0;
 }
 
@@ -218,15 +116,20 @@ scram_H(const uint8 *input, int len, uint8 *result)
 int
 scram_ClientKey(const uint8 *salted_password, uint8 *result)
 {
-	scram_HMAC_ctx ctx;
+	pg_hmac_ctx *ctx = pg_hmac_create(PG_SHA256);
+
+	if (ctx == NULL)
+		return -1;
 
-	if (scram_HMAC_init(&ctx, salted_password, SCRAM_KEY_LEN) < 0 ||
-		scram_HMAC_update(&ctx, "Client Key", strlen("Client Key")) < 0 ||
-		scram_HMAC_final(result, &ctx) < 0)
+	if (pg_hmac_init(ctx, salted_password, SCRAM_KEY_LEN) < 0 ||
+		pg_hmac_update(ctx, (uint8 *) "Client Key", strlen("Client Key")) < 0 ||
+		pg_hmac_final(ctx, result, SCRAM_KEY_LEN) < 0)
 	{
+		pg_hmac_free(ctx);
 		return -1;
 	}
 
+	pg_hmac_free(ctx);
 	return 0;
 }
 
@@ -236,15 +139,20 @@ scram_ClientKey(const uint8 *salted_password, uint8 *result)
 int
 scram_ServerKey(const uint8 *salted_password, uint8 *result)
 {
-	scram_HMAC_ctx ctx;
+	pg_hmac_ctx *ctx = pg_hmac_create(PG_SHA256);
+
+	if (ctx == NULL)
+		return -1;
 
-	if (scram_HMAC_init(&ctx, salted_password, SCRAM_KEY_LEN) < 0 ||
-		scram_HMAC_update(&ctx, "Server Key", strlen("Server Key")) < 0 ||
-		scram_HMAC_final(result, &ctx) < 0)
+	if (pg_hmac_init(ctx, salted_password, SCRAM_KEY_LEN) < 0 ||
+		pg_hmac_update(ctx, (uint8 *) "Server Key", strlen("Server Key")) < 0 ||
+		pg_hmac_final(ctx, result, SCRAM_KEY_LEN) < 0)
 	{
+		pg_hmac_free(ctx);
 		return -1;
 	}
 
+	pg_hmac_free(ctx);
 	return 0;
 }