hkdf.c
/*
* Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* HMAC low level APIs are deprecated for public use, but still ok for internal
* use.
*/
#include "internal/deprecated.h"
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/kdf.h>
#include <openssl/core_names.h>
#include "internal/cryptlib.h"
#include "internal/numbers.h"
#include "crypto/evp.h"
#include "prov/provider_ctx.h"
#include "prov/providercommon.h"
#include "prov/providercommonerr.h"
#include "prov/implementations.h"
#include "prov/provider_util.h"
#include "e_os.h"
#define HKDF_MAXBUF 1024
static OSSL_FUNC_kdf_newctx_fn kdf_hkdf_new;
static OSSL_FUNC_kdf_freectx_fn kdf_hkdf_free;
static OSSL_FUNC_kdf_reset_fn kdf_hkdf_reset;
static OSSL_FUNC_kdf_derive_fn kdf_hkdf_derive;
static OSSL_FUNC_kdf_settable_ctx_params_fn kdf_hkdf_settable_ctx_params;
static OSSL_FUNC_kdf_set_ctx_params_fn kdf_hkdf_set_ctx_params;
static OSSL_FUNC_kdf_gettable_ctx_params_fn kdf_hkdf_gettable_ctx_params;
static OSSL_FUNC_kdf_get_ctx_params_fn kdf_hkdf_get_ctx_params;
static int HKDF(const EVP_MD *evp_md,
const unsigned char *salt, size_t salt_len,
const unsigned char *key, size_t key_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len);
static int HKDF_Extract(const EVP_MD *evp_md,
const unsigned char *salt, size_t salt_len,
const unsigned char *ikm, size_t ikm_len,
unsigned char *prk, size_t prk_len);
static int HKDF_Expand(const EVP_MD *evp_md,
const unsigned char *prk, size_t prk_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len);
typedef struct {
void *provctx;
int mode;
PROV_DIGEST digest;
unsigned char *salt;
size_t salt_len;
unsigned char *key;
size_t key_len;
unsigned char info[HKDF_MAXBUF];
size_t info_len;
} KDF_HKDF;
static void *kdf_hkdf_new(void *provctx)
{
KDF_HKDF *ctx;
if (!ossl_prov_is_running())
return NULL;
if ((ctx = OPENSSL_zalloc(sizeof(*ctx))) == NULL)
ERR_raise(ERR_LIB_PROV, ERR_R_MALLOC_FAILURE);
else
ctx->provctx = provctx;
return ctx;
}
static void kdf_hkdf_free(void *vctx)
{
KDF_HKDF *ctx = (KDF_HKDF *)vctx;
if (ctx != NULL) {
kdf_hkdf_reset(ctx);
OPENSSL_free(ctx);
}
}
static void kdf_hkdf_reset(void *vctx)
{
KDF_HKDF *ctx = (KDF_HKDF *)vctx;
void *provctx = ctx->provctx;
ossl_prov_digest_reset(&ctx->digest);
OPENSSL_free(ctx->salt);
OPENSSL_clear_free(ctx->key, ctx->key_len);
OPENSSL_cleanse(ctx->info, ctx->info_len);
memset(ctx, 0, sizeof(*ctx));
ctx->provctx = provctx;
}
static size_t kdf_hkdf_size(KDF_HKDF *ctx)
{
int sz;
const EVP_MD *md = ossl_prov_digest_md(&ctx->digest);
if (ctx->mode != EVP_KDF_HKDF_MODE_EXTRACT_ONLY)
return SIZE_MAX;
if (md == NULL) {
ERR_raise(ERR_LIB_PROV, PROV_R_MISSING_MESSAGE_DIGEST);
return 0;
}
sz = EVP_MD_size(md);
if (sz < 0)
return 0;
return sz;
}
static int kdf_hkdf_derive(void *vctx, unsigned char *key, size_t keylen)
{
KDF_HKDF *ctx = (KDF_HKDF *)vctx;
const EVP_MD *md;
if (!ossl_prov_is_running())
return 0;
md = ossl_prov_digest_md(&ctx->digest);
if (md == NULL) {
ERR_raise(ERR_LIB_PROV, PROV_R_MISSING_MESSAGE_DIGEST);
return 0;
}
if (ctx->key == NULL) {
ERR_raise(ERR_LIB_PROV, PROV_R_MISSING_KEY);
return 0;
}
if (keylen == 0) {
ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_KEY_LENGTH);
return 0;
}
switch (ctx->mode) {
case EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND:
return HKDF(md, ctx->salt, ctx->salt_len, ctx->key,
ctx->key_len, ctx->info, ctx->info_len, key,
keylen);
case EVP_KDF_HKDF_MODE_EXTRACT_ONLY:
return HKDF_Extract(md, ctx->salt, ctx->salt_len, ctx->key,
ctx->key_len, key, keylen);
case EVP_KDF_HKDF_MODE_EXPAND_ONLY:
return HKDF_Expand(md, ctx->key, ctx->key_len, ctx->info,
ctx->info_len, key, keylen);
default:
return 0;
}
}
static int kdf_hkdf_set_ctx_params(void *vctx, const OSSL_PARAM params[])
{
const OSSL_PARAM *p;
KDF_HKDF *ctx = vctx;
OSSL_LIB_CTX *provctx = PROV_LIBCTX_OF(ctx->provctx);
int n;
if (!ossl_prov_digest_load_from_params(&ctx->digest, params, provctx))
return 0;
if ((p = OSSL_PARAM_locate_const(params, OSSL_KDF_PARAM_MODE)) != NULL) {
if (p->data_type == OSSL_PARAM_UTF8_STRING) {
if (strcasecmp(p->data, "EXTRACT_AND_EXPAND") == 0) {
ctx->mode = EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND;
} else if (strcasecmp(p->data, "EXTRACT_ONLY") == 0) {
ctx->mode = EVP_KDF_HKDF_MODE_EXTRACT_ONLY;
} else if (strcasecmp(p->data, "EXPAND_ONLY") == 0) {
ctx->mode = EVP_KDF_HKDF_MODE_EXPAND_ONLY;
} else {
ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);
return 0;
}
} else if (OSSL_PARAM_get_int(p, &n)) {
if (n != EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND
&& n != EVP_KDF_HKDF_MODE_EXTRACT_ONLY
&& n != EVP_KDF_HKDF_MODE_EXPAND_ONLY) {
ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);
return 0;
}
ctx->mode = n;
} else {
ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);
return 0;
}
}
if ((p = OSSL_PARAM_locate_const(params, OSSL_KDF_PARAM_KEY)) != NULL) {
OPENSSL_clear_free(ctx->key, ctx->key_len);
ctx->key = NULL;
if (!OSSL_PARAM_get_octet_string(p, (void **)&ctx->key, 0,
&ctx->key_len))
return 0;
}
if ((p = OSSL_PARAM_locate_const(params, OSSL_KDF_PARAM_SALT)) != NULL) {
if (p->data_size != 0 && p->data != NULL) {
OPENSSL_free(ctx->salt);
ctx->salt = NULL;
if (!OSSL_PARAM_get_octet_string(p, (void **)&ctx->salt, 0,
&ctx->salt_len))
return 0;
}
}
/* The info fields concatenate, so process them all */
if ((p = OSSL_PARAM_locate_const(params, OSSL_KDF_PARAM_INFO)) != NULL) {
ctx->info_len = 0;
for (; p != NULL; p = OSSL_PARAM_locate_const(p + 1,
OSSL_KDF_PARAM_INFO)) {
const void *q = ctx->info + ctx->info_len;
size_t sz = 0;
if (p->data_size != 0
&& p->data != NULL
&& !OSSL_PARAM_get_octet_string(p, (void **)&q,
HKDF_MAXBUF - ctx->info_len,
&sz))
return 0;
ctx->info_len += sz;
}
}
return 1;
}
static const OSSL_PARAM *kdf_hkdf_settable_ctx_params(ossl_unused void *provctx)
{
static const OSSL_PARAM known_settable_ctx_params[] = {
OSSL_PARAM_utf8_string(OSSL_KDF_PARAM_MODE, NULL, 0),
OSSL_PARAM_int(OSSL_KDF_PARAM_MODE, NULL),
OSSL_PARAM_utf8_string(OSSL_KDF_PARAM_PROPERTIES, NULL, 0),
OSSL_PARAM_utf8_string(OSSL_KDF_PARAM_DIGEST, NULL, 0),
OSSL_PARAM_octet_string(OSSL_KDF_PARAM_SALT, NULL, 0),
OSSL_PARAM_octet_string(OSSL_KDF_PARAM_KEY, NULL, 0),
OSSL_PARAM_octet_string(OSSL_KDF_PARAM_INFO, NULL, 0),
OSSL_PARAM_END
};
return known_settable_ctx_params;
}
static int kdf_hkdf_get_ctx_params(void *vctx, OSSL_PARAM params[])
{
KDF_HKDF *ctx = (KDF_HKDF *)vctx;
OSSL_PARAM *p;
if ((p = OSSL_PARAM_locate(params, OSSL_KDF_PARAM_SIZE)) != NULL)
return OSSL_PARAM_set_size_t(p, kdf_hkdf_size(ctx));
return -2;
}
static const OSSL_PARAM *kdf_hkdf_gettable_ctx_params(ossl_unused void *provctx)
{
static const OSSL_PARAM known_gettable_ctx_params[] = {
OSSL_PARAM_size_t(OSSL_KDF_PARAM_SIZE, NULL),
OSSL_PARAM_END
};
return known_gettable_ctx_params;
}
const OSSL_DISPATCH ossl_kdf_hkdf_functions[] = {
{ OSSL_FUNC_KDF_NEWCTX, (void(*)(void))kdf_hkdf_new },
{ OSSL_FUNC_KDF_FREECTX, (void(*)(void))kdf_hkdf_free },
{ OSSL_FUNC_KDF_RESET, (void(*)(void))kdf_hkdf_reset },
{ OSSL_FUNC_KDF_DERIVE, (void(*)(void))kdf_hkdf_derive },
{ OSSL_FUNC_KDF_SETTABLE_CTX_PARAMS,
(void(*)(void))kdf_hkdf_settable_ctx_params },
{ OSSL_FUNC_KDF_SET_CTX_PARAMS, (void(*)(void))kdf_hkdf_set_ctx_params },
{ OSSL_FUNC_KDF_GETTABLE_CTX_PARAMS,
(void(*)(void))kdf_hkdf_gettable_ctx_params },
{ OSSL_FUNC_KDF_GET_CTX_PARAMS, (void(*)(void))kdf_hkdf_get_ctx_params },
{ 0, NULL }
};
/*
* Refer to "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)"
* Section 2 (https://tools.ietf.org/html/rfc5869#section-2) and
* "Cryptographic Extraction and Key Derivation: The HKDF Scheme"
* Section 4.2 (https://eprint.iacr.org/2010/264.pdf).
*
* From the paper:
* The scheme HKDF is specified as:
* HKDF(XTS, SKM, CTXinfo, L) = K(1) | K(2) | ... | K(t)
*
* where:
* SKM is source key material
* XTS is extractor salt (which may be null or constant)
* CTXinfo is context information (may be null)
* L is the number of key bits to be produced by KDF
* k is the output length in bits of the hash function used with HMAC
* t = ceil(L/k)
* the value K(t) is truncated to its first d = L mod k bits.
*
* From RFC 5869:
* 2.2. Step 1: Extract
* HKDF-Extract(salt, IKM) -> PRK
* 2.3. Step 2: Expand
* HKDF-Expand(PRK, info, L) -> OKM
*/
static int HKDF(const EVP_MD *evp_md,
const unsigned char *salt, size_t salt_len,
const unsigned char *ikm, size_t ikm_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len)
{
unsigned char prk[EVP_MAX_MD_SIZE];
int ret, sz;
size_t prk_len;
sz = EVP_MD_size(evp_md);
if (sz < 0)
return 0;
prk_len = (size_t)sz;
/* Step 1: HKDF-Extract(salt, IKM) -> PRK */
if (!HKDF_Extract(evp_md, salt, salt_len, ikm, ikm_len, prk, prk_len))
return 0;
/* Step 2: HKDF-Expand(PRK, info, L) -> OKM */
ret = HKDF_Expand(evp_md, prk, prk_len, info, info_len, okm, okm_len);
OPENSSL_cleanse(prk, sizeof(prk));
return ret;
}
/*
* Refer to "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)"
* Section 2.2 (https://tools.ietf.org/html/rfc5869#section-2.2).
*
* 2.2. Step 1: Extract
*
* HKDF-Extract(salt, IKM) -> PRK
*
* Options:
* Hash a hash function; HashLen denotes the length of the
* hash function output in octets
*
* Inputs:
* salt optional salt value (a non-secret random value);
* if not provided, it is set to a string of HashLen zeros.
* IKM input keying material
*
* Output:
* PRK a pseudorandom key (of HashLen octets)
*
* The output PRK is calculated as follows:
*
* PRK = HMAC-Hash(salt, IKM)
*/
static int HKDF_Extract(const EVP_MD *evp_md,
const unsigned char *salt, size_t salt_len,
const unsigned char *ikm, size_t ikm_len,
unsigned char *prk, size_t prk_len)
{
int sz = EVP_MD_size(evp_md);
if (sz < 0)
return 0;
if (prk_len != (size_t)sz) {
ERR_raise(ERR_LIB_PROV, PROV_R_WRONG_OUTPUT_BUFFER_SIZE);
return 0;
}
/* calc: PRK = HMAC-Hash(salt, IKM) */
return HMAC(evp_md, salt, salt_len, ikm, ikm_len, prk, NULL) != NULL;
}
/*
* Refer to "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)"
* Section 2.3 (https://tools.ietf.org/html/rfc5869#section-2.3).
*
* 2.3. Step 2: Expand
*
* HKDF-Expand(PRK, info, L) -> OKM
*
* Options:
* Hash a hash function; HashLen denotes the length of the
* hash function output in octets
*
* Inputs:
* PRK a pseudorandom key of at least HashLen octets
* (usually, the output from the extract step)
* info optional context and application specific information
* (can be a zero-length string)
* L length of output keying material in octets
* (<= 255*HashLen)
*
* Output:
* OKM output keying material (of L octets)
*
* The output OKM is calculated as follows:
*
* N = ceil(L/HashLen)
* T = T(1) | T(2) | T(3) | ... | T(N)
* OKM = first L octets of T
*
* where:
* T(0) = empty string (zero length)
* T(1) = HMAC-Hash(PRK, T(0) | info | 0x01)
* T(2) = HMAC-Hash(PRK, T(1) | info | 0x02)
* T(3) = HMAC-Hash(PRK, T(2) | info | 0x03)
* ...
*
* (where the constant concatenated to the end of each T(n) is a
* single octet.)
*/
static int HKDF_Expand(const EVP_MD *evp_md,
const unsigned char *prk, size_t prk_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len)
{
HMAC_CTX *hmac;
int ret = 0, sz;
unsigned int i;
unsigned char prev[EVP_MAX_MD_SIZE];
size_t done_len = 0, dig_len, n;
sz = EVP_MD_size(evp_md);
if (sz <= 0)
return 0;
dig_len = (size_t)sz;
/* calc: N = ceil(L/HashLen) */
n = okm_len / dig_len;
if (okm_len % dig_len)
n++;
if (n > 255 || okm == NULL)
return 0;
if ((hmac = HMAC_CTX_new()) == NULL)
return 0;
if (!HMAC_Init_ex(hmac, prk, prk_len, evp_md, NULL))
goto err;
for (i = 1; i <= n; i++) {
size_t copy_len;
const unsigned char ctr = i;
/* calc: T(i) = HMAC-Hash(PRK, T(i - 1) | info | i) */
if (i > 1) {
if (!HMAC_Init_ex(hmac, NULL, 0, NULL, NULL))
goto err;
if (!HMAC_Update(hmac, prev, dig_len))
goto err;
}
if (!HMAC_Update(hmac, info, info_len))
goto err;
if (!HMAC_Update(hmac, &ctr, 1))
goto err;
if (!HMAC_Final(hmac, prev, NULL))
goto err;
copy_len = (done_len + dig_len > okm_len) ?
okm_len - done_len :
dig_len;
memcpy(okm + done_len, prev, copy_len);
done_len += copy_len;
}
ret = 1;
err:
OPENSSL_cleanse(prev, sizeof(prev));
HMAC_CTX_free(hmac);
return ret;
}
