1 files changed, 274 insertions, 0 deletions
diff --git a/src/common/scram-common.c b/src/common/scram-common.c
new file mode 100644
index 0000000..69a96f6
--- /dev/null
+++ b/src/common/scram-common.c
@@ -0,0 +1,274 @@
+/*-------------------------------------------------------------------------
+ * scram-common.c
+ *		Shared frontend/backend code for SCRAM authentication
+ *
+ * This contains the common low-level functions needed in both frontend and
+ * backend, for implement the Salted Challenge Response Authentication
+ * Mechanism (SCRAM), per IETF's RFC 5802.
+ *
+ * Portions Copyright (c) 2017-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/common/scram-common.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include "common/base64.h"
+#include "common/hmac.h"
+#include "common/scram-common.h"
+#include "port/pg_bswap.h"
+
+/*
+ * Calculate SaltedPassword.
+ *
+ * The password should already be normalized by SASLprep.  Returns 0 on
+ * success, -1 on failure.
+ */
+int
+scram_SaltedPassword(const char *password,
+					 const char *salt, int saltlen, int iterations,
+					 uint8 *result)
+{
+	int			password_len = strlen(password);
+	uint32		one = pg_hton32(1);
+	int			i,
+				j;
+	uint8		Ui[SCRAM_KEY_LEN];
+	uint8		Ui_prev[SCRAM_KEY_LEN];
+	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
+	 * essentially PBKDF2 (see RFC2898) with HMAC() as the pseudorandom
+	 * function.
+	 */
+
+	/* First iteration */
+	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;
+	}
+
+	memcpy(result, Ui_prev, SCRAM_KEY_LEN);
+
+	/* Subsequent iterations */
+	for (i = 2; i <= iterations; i++)
+	{
+		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;
+		}
+
+		for (j = 0; j < SCRAM_KEY_LEN; j++)
+			result[j] ^= Ui[j];
+		memcpy(Ui_prev, Ui, SCRAM_KEY_LEN);
+	}
+
+	pg_hmac_free(hmac_ctx);
+	return 0;
+}
+
+
+/*
+ * Calculate SHA-256 hash for a NULL-terminated string. (The NULL terminator is
+ * not included in the hash).  Returns 0 on success, -1 on failure.
+ */
+int
+scram_H(const uint8 *input, int len, uint8 *result)
+{
+	pg_cryptohash_ctx *ctx;
+
+	ctx = pg_cryptohash_create(PG_SHA256);
+	if (ctx == NULL)
+		return -1;
+
+	if (pg_cryptohash_init(ctx) < 0 ||
+		pg_cryptohash_update(ctx, input, len) < 0 ||
+		pg_cryptohash_final(ctx, result, SCRAM_KEY_LEN) < 0)
+	{
+		pg_cryptohash_free(ctx);
+		return -1;
+	}
+
+	pg_cryptohash_free(ctx);
+	return 0;
+}
+
+/*
+ * Calculate ClientKey.  Returns 0 on success, -1 on failure.
+ */
+int
+scram_ClientKey(const uint8 *salted_password, uint8 *result)
+{
+	pg_hmac_ctx *ctx = pg_hmac_create(PG_SHA256);
+
+	if (ctx == NULL)
+		return -1;
+
+	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;
+}
+
+/*
+ * Calculate ServerKey.  Returns 0 on success, -1 on failure.
+ */
+int
+scram_ServerKey(const uint8 *salted_password, uint8 *result)
+{
+	pg_hmac_ctx *ctx = pg_hmac_create(PG_SHA256);
+
+	if (ctx == NULL)
+		return -1;
+
+	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;
+}
+
+
+/*
+ * Construct a SCRAM secret, for storing in pg_authid.rolpassword.
+ *
+ * The password should already have been processed with SASLprep, if necessary!
+ *
+ * If iterations is 0, default number of iterations is used.  The result is
+ * palloc'd or malloc'd, so caller is responsible for freeing it.
+ */
+char *
+scram_build_secret(const char *salt, int saltlen, int iterations,
+				   const char *password)
+{
+	uint8		salted_password[SCRAM_KEY_LEN];
+	uint8		stored_key[SCRAM_KEY_LEN];
+	uint8		server_key[SCRAM_KEY_LEN];
+	char	   *result;
+	char	   *p;
+	int			maxlen;
+	int			encoded_salt_len;
+	int			encoded_stored_len;
+	int			encoded_server_len;
+	int			encoded_result;
+
+	if (iterations <= 0)
+		iterations = SCRAM_DEFAULT_ITERATIONS;
+
+	/* Calculate StoredKey and ServerKey */
+	if (scram_SaltedPassword(password, salt, saltlen, iterations,
+							 salted_password) < 0 ||
+		scram_ClientKey(salted_password, stored_key) < 0 ||
+		scram_H(stored_key, SCRAM_KEY_LEN, stored_key) < 0 ||
+		scram_ServerKey(salted_password, server_key) < 0)
+	{
+#ifdef FRONTEND
+		return NULL;
+#else
+		elog(ERROR, "could not calculate stored key and server key");
+#endif
+	}
+
+	/*----------
+	 * The format is:
+	 * SCRAM-SHA-256$<iteration count>:<salt>$<StoredKey>:<ServerKey>
+	 *----------
+	 */
+	encoded_salt_len = pg_b64_enc_len(saltlen);
+	encoded_stored_len = pg_b64_enc_len(SCRAM_KEY_LEN);
+	encoded_server_len = pg_b64_enc_len(SCRAM_KEY_LEN);
+
+	maxlen = strlen("SCRAM-SHA-256") + 1
+		+ 10 + 1				/* iteration count */
+		+ encoded_salt_len + 1	/* Base64-encoded salt */
+		+ encoded_stored_len + 1	/* Base64-encoded StoredKey */
+		+ encoded_server_len + 1;	/* Base64-encoded ServerKey */
+
+#ifdef FRONTEND
+	result = malloc(maxlen);
+	if (!result)
+		return NULL;
+#else
+	result = palloc(maxlen);
+#endif
+
+	p = result + sprintf(result, "SCRAM-SHA-256$%d:", iterations);
+
+	/* salt */
+	encoded_result = pg_b64_encode(salt, saltlen, p, encoded_salt_len);
+	if (encoded_result < 0)
+	{
+#ifdef FRONTEND
+		free(result);
+		return NULL;
+#else
+		elog(ERROR, "could not encode salt");
+#endif
+	}
+	p += encoded_result;
+	*(p++) = '$';
+
+	/* stored key */
+	encoded_result = pg_b64_encode((char *) stored_key, SCRAM_KEY_LEN, p,
+								   encoded_stored_len);
+	if (encoded_result < 0)
+	{
+#ifdef FRONTEND
+		free(result);
+		return NULL;
+#else
+		elog(ERROR, "could not encode stored key");
+#endif
+	}
+
+	p += encoded_result;
+	*(p++) = ':';
+
+	/* server key */
+	encoded_result = pg_b64_encode((char *) server_key, SCRAM_KEY_LEN, p,
+								   encoded_server_len);
+	if (encoded_result < 0)
+	{
+#ifdef FRONTEND
+		free(result);
+		return NULL;
+#else
+		elog(ERROR, "could not encode server key");
+#endif
+	}
+
+	p += encoded_result;
+	*(p++) = '\0';
+
+	Assert(p - result <= maxlen);
+
+	return result;
+}