hmac.c

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/*-------------------------------------------------------------------------
 *
 * hmac.c
 *    Implements Keyed-Hashing for Message Authentication (HMAC)
 *
 * Fallback implementation of HMAC, as specified in RFC 2104.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/common/hmac.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include "common/cryptohash.h"
#include "common/hmac.h"
#include "common/md5.h"
#include "common/sha1.h"
#include "common/sha2.h"
 
/*
 * In backend, use palloc/pfree to ease the error handling.  In frontend,
 * use malloc to be able to return a failure status back to the caller.
 */
#ifndef FRONTEND
#define ALLOC(size) palloc(size)
#define FREE(ptr) pfree(ptr)
#else
#define ALLOC(size) malloc(size)
#define FREE(ptr) free(ptr)
#endif
 
/* Set of error states */
typedef enum pg_hmac_errno
{
    PG_HMAC_ERROR_NONE = 0,
    PG_HMAC_ERROR_OOM,
    PG_HMAC_ERROR_INTERNAL,
} pg_hmac_errno;
 
/* Internal pg_hmac_ctx structure */
struct pg_hmac_ctx
{
    pg_cryptohash_ctx *hash;
    pg_cryptohash_type type;
    pg_hmac_errno error;
    const char *errreason;
    int         block_size;
    int         digest_size;
 
    /*
     * Use the largest block size among supported options.  This wastes some
     * memory but simplifies the allocation logic.
     */
    uint8       k_ipad[PG_SHA512_BLOCK_LENGTH];
    uint8       k_opad[PG_SHA512_BLOCK_LENGTH];
};
 
#define HMAC_IPAD 0x36
#define HMAC_OPAD 0x5C
 
/*
 * pg_hmac_create
 *
 * Allocate a hash context.  Returns NULL on failure for an OOM.  The
 * backend issues an error, without returning.
 */
pg_hmac_ctx *
pg_hmac_create(pg_cryptohash_type type)
{
    pg_hmac_ctx *ctx;
 
    ctx = ALLOC(sizeof(pg_hmac_ctx));
    if (ctx == NULL)
        return NULL;
    memset(ctx, 0, sizeof(pg_hmac_ctx));
    ctx->type = type;
    ctx->error = PG_HMAC_ERROR_NONE;
    ctx->errreason = NULL;
 
    /*
     * Initialize the context data.  This requires to know the digest and
     * block lengths, that depend on the type of hash used.
     */
    switch (type)
    {
        case PG_MD5:
            ctx->digest_size = MD5_DIGEST_LENGTH;
            ctx->block_size = MD5_BLOCK_SIZE;
            break;
        case PG_SHA1:
            ctx->digest_size = SHA1_DIGEST_LENGTH;
            ctx->block_size = SHA1_BLOCK_SIZE;
            break;
        case PG_SHA224:
            ctx->digest_size = PG_SHA224_DIGEST_LENGTH;
            ctx->block_size = PG_SHA224_BLOCK_LENGTH;
            break;
        case PG_SHA256:
            ctx->digest_size = PG_SHA256_DIGEST_LENGTH;
            ctx->block_size = PG_SHA256_BLOCK_LENGTH;
            break;
        case PG_SHA384:
            ctx->digest_size = PG_SHA384_DIGEST_LENGTH;
            ctx->block_size = PG_SHA384_BLOCK_LENGTH;
            break;
        case PG_SHA512:
            ctx->digest_size = PG_SHA512_DIGEST_LENGTH;
            ctx->block_size = PG_SHA512_BLOCK_LENGTH;
            break;
    }
 
    ctx->hash = pg_cryptohash_create(type);
    if (ctx->hash == NULL)
    {
        explicit_bzero(ctx, sizeof(pg_hmac_ctx));
        FREE(ctx);
        return NULL;
    }
 
    return ctx;
}
 
/*
 * pg_hmac_init
 *
 * Initialize a HMAC context.  Returns 0 on success, -1 on failure.
 */
int
pg_hmac_init(pg_hmac_ctx *ctx, const uint8 *key, size_t len)
{
    int         digest_size;
    int         block_size;
    uint8      *shrinkbuf = NULL;
 
    if (ctx == NULL)
        return -1;
 
    digest_size = ctx->digest_size;
    block_size = ctx->block_size;
 
    memset(ctx->k_opad, HMAC_OPAD, ctx->block_size);
    memset(ctx->k_ipad, HMAC_IPAD, ctx->block_size);
 
    /*
     * If the key is longer than the block size, pass it through the hash once
     * to shrink it down.
     */
    if (len > block_size)
    {
        pg_cryptohash_ctx *hash_ctx;
 
        /* temporary buffer for one-time shrink */
        shrinkbuf = ALLOC(digest_size);
        if (shrinkbuf == NULL)
        {
            ctx->error = PG_HMAC_ERROR_OOM;
            return -1;
        }
        memset(shrinkbuf, 0, digest_size);
 
        hash_ctx = pg_cryptohash_create(ctx->type);
        if (hash_ctx == NULL)
        {
            ctx->error = PG_HMAC_ERROR_OOM;
            FREE(shrinkbuf);
            return -1;
        }
 
        if (pg_cryptohash_init(hash_ctx) < 0 ||
            pg_cryptohash_update(hash_ctx, key, len) < 0 ||
            pg_cryptohash_final(hash_ctx, shrinkbuf, digest_size) < 0)
        {
            ctx->error = PG_HMAC_ERROR_INTERNAL;
            ctx->errreason = pg_cryptohash_error(hash_ctx);
            pg_cryptohash_free(hash_ctx);
            FREE(shrinkbuf);
            return -1;
        }
 
        key = shrinkbuf;
        len = digest_size;
        pg_cryptohash_free(hash_ctx);
    }
 
    for (size_t i = 0; i < len; i++)
    {
        ctx->k_ipad[i] ^= key[i];
        ctx->k_opad[i] ^= key[i];
    }
 
    /* tmp = H(K XOR ipad, text) */
    if (pg_cryptohash_init(ctx->hash) < 0 ||
        pg_cryptohash_update(ctx->hash, ctx->k_ipad, ctx->block_size) < 0)
    {
        ctx->error = PG_HMAC_ERROR_INTERNAL;
        ctx->errreason = pg_cryptohash_error(ctx->hash);
        if (shrinkbuf)
            FREE(shrinkbuf);
        return -1;
    }
 
    if (shrinkbuf)
        FREE(shrinkbuf);
    return 0;
}
 
/*
 * pg_hmac_update
 *
 * Update a HMAC context.  Returns 0 on success, -1 on failure.
 */
int
pg_hmac_update(pg_hmac_ctx *ctx, const uint8 *data, size_t len)
{
    if (ctx == NULL)
        return -1;
 
    if (pg_cryptohash_update(ctx->hash, data, len) < 0)
    {
        ctx->error = PG_HMAC_ERROR_INTERNAL;
        ctx->errreason = pg_cryptohash_error(ctx->hash);
        return -1;
    }
 
    return 0;
}
 
/*
 * pg_hmac_final
 *
 * Finalize a HMAC context.  Returns 0 on success, -1 on failure.
 */
int
pg_hmac_final(pg_hmac_ctx *ctx, uint8 *dest, size_t len)
{
    uint8      *h;
 
    if (ctx == NULL)
        return -1;
 
    h = ALLOC(ctx->digest_size);
    if (h == NULL)
    {
        ctx->error = PG_HMAC_ERROR_OOM;
        return -1;
    }
    memset(h, 0, ctx->digest_size);
 
    if (pg_cryptohash_final(ctx->hash, h, ctx->digest_size) < 0)
    {
        ctx->error = PG_HMAC_ERROR_INTERNAL;
        ctx->errreason = pg_cryptohash_error(ctx->hash);
        FREE(h);
        return -1;
    }
 
    /* H(K XOR opad, tmp) */
    if (pg_cryptohash_init(ctx->hash) < 0 ||
        pg_cryptohash_update(ctx->hash, ctx->k_opad, ctx->block_size) < 0 ||
        pg_cryptohash_update(ctx->hash, h, ctx->digest_size) < 0 ||
        pg_cryptohash_final(ctx->hash, dest, len) < 0)
    {
        ctx->error = PG_HMAC_ERROR_INTERNAL;
        ctx->errreason = pg_cryptohash_error(ctx->hash);
        FREE(h);
        return -1;
    }
 
    FREE(h);
    return 0;
}
 
/*
 * pg_hmac_free
 *
 * Free a HMAC context.
 */
void
pg_hmac_free(pg_hmac_ctx *ctx)
{
    if (ctx == NULL)
        return;
 
    pg_cryptohash_free(ctx->hash);
    explicit_bzero(ctx, sizeof(pg_hmac_ctx));
    FREE(ctx);
}
 
/*
 * pg_hmac_error
 *
 * Returns a static string providing details about an error that happened
 * during a HMAC computation.
 */
const char *
pg_hmac_error(pg_hmac_ctx *ctx)
{
    if (ctx == NULL)
        return _("out of memory");
 
    /*
     * If a reason is provided, rely on it, else fallback to any error code
     * set.
     */
    if (ctx->errreason)
        return ctx->errreason;
 
    switch (ctx->error)
    {
        case PG_HMAC_ERROR_NONE:
            return _("success");
        case PG_HMAC_ERROR_INTERNAL:
            return _("internal error");
        case PG_HMAC_ERROR_OOM:
            return _("out of memory");
    }
 
    Assert(false);              /* cannot be reached */
    return _("success");
}