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openssl/crypto/kdf/hkdf.c
David Makepeace e70185883e Added algorithm description comments to HKDF. 
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8994)
2019-05-24 10:09:37 +10:00

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/*
* Copyright 2016-2018 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
*/
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/kdf.h>
#include "internal/cryptlib.h"
#include "internal/numbers.h"
#include "internal/evp_int.h"
#include "kdf_local.h"
#define HKDF_MAXBUF 1024
static void kdf_hkdf_reset(EVP_KDF_IMPL *impl);
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);
struct evp_kdf_impl_st {
int mode;
const EVP_MD *md;
unsigned char *salt;
size_t salt_len;
unsigned char *key;
size_t key_len;
unsigned char info[HKDF_MAXBUF];
size_t info_len;
};
static EVP_KDF_IMPL *kdf_hkdf_new(void)
{
EVP_KDF_IMPL *impl;
if ((impl = OPENSSL_zalloc(sizeof(*impl))) == NULL)
KDFerr(KDF_F_KDF_HKDF_NEW, ERR_R_MALLOC_FAILURE);
return impl;
}
static void kdf_hkdf_free(EVP_KDF_IMPL *impl)
{
kdf_hkdf_reset(impl);
OPENSSL_free(impl);
}
static void kdf_hkdf_reset(EVP_KDF_IMPL *impl)
{
OPENSSL_free(impl->salt);
OPENSSL_clear_free(impl->key, impl->key_len);
OPENSSL_cleanse(impl->info, impl->info_len);
memset(impl, 0, sizeof(*impl));
}
static int kdf_hkdf_ctrl(EVP_KDF_IMPL *impl, int cmd, va_list args)
{
const unsigned char *p;
size_t len;
const EVP_MD *md;
switch (cmd) {
case EVP_KDF_CTRL_SET_MD:
md = va_arg(args, const EVP_MD *);
if (md == NULL)
return 0;
impl->md = md;
return 1;
case EVP_KDF_CTRL_SET_HKDF_MODE:
impl->mode = va_arg(args, int);
return 1;
case EVP_KDF_CTRL_SET_SALT:
p = va_arg(args, const unsigned char *);
len = va_arg(args, size_t);
if (len == 0 || p == NULL)
return 1;
OPENSSL_free(impl->salt);
impl->salt = OPENSSL_memdup(p, len);
if (impl->salt == NULL)
return 0;
impl->salt_len = len;
return 1;
case EVP_KDF_CTRL_SET_KEY:
p = va_arg(args, const unsigned char *);
len = va_arg(args, size_t);
OPENSSL_clear_free(impl->key, impl->key_len);
impl->key = OPENSSL_memdup(p, len);
if (impl->key == NULL)
return 0;
impl->key_len = len;
return 1;
case EVP_KDF_CTRL_RESET_HKDF_INFO:
OPENSSL_cleanse(impl->info, impl->info_len);
impl->info_len = 0;
return 1;
case EVP_KDF_CTRL_ADD_HKDF_INFO:
p = va_arg(args, const unsigned char *);
len = va_arg(args, size_t);
if (len == 0 || p == NULL)
return 1;
if (len > (HKDF_MAXBUF - impl->info_len))
return 0;
memcpy(impl->info + impl->info_len, p, len);
impl->info_len += len;
return 1;
default:
return -2;
}
}
static int kdf_hkdf_ctrl_str(EVP_KDF_IMPL *impl, const char *type,
const char *value)
{
if (strcmp(type, "mode") == 0) {
int mode;
if (strcmp(value, "EXTRACT_AND_EXPAND") == 0)
mode = EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND;
else if (strcmp(value, "EXTRACT_ONLY") == 0)
mode = EVP_KDF_HKDF_MODE_EXTRACT_ONLY;
else if (strcmp(value, "EXPAND_ONLY") == 0)
mode = EVP_KDF_HKDF_MODE_EXPAND_ONLY;
else
return 0;
return call_ctrl(kdf_hkdf_ctrl, impl, EVP_KDF_CTRL_SET_HKDF_MODE, mode);
}
if (strcmp(type, "digest") == 0)
return kdf_md2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_SET_MD, value);
if (strcmp(type, "salt") == 0)
return kdf_str2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_SET_SALT, value);
if (strcmp(type, "hexsalt") == 0)
return kdf_hex2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_SET_SALT, value);
if (strcmp(type, "key") == 0)
return kdf_str2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_SET_KEY, value);
if (strcmp(type, "hexkey") == 0)
return kdf_hex2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_SET_KEY, value);
if (strcmp(type, "info") == 0)
return kdf_str2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_ADD_HKDF_INFO,
value);
if (strcmp(type, "hexinfo") == 0)
return kdf_hex2ctrl(impl, kdf_hkdf_ctrl, EVP_KDF_CTRL_ADD_HKDF_INFO,
value);
return -2;
}
static size_t kdf_hkdf_size(EVP_KDF_IMPL *impl)
{
int sz;
if (impl->mode != EVP_KDF_HKDF_MODE_EXTRACT_ONLY)
return SIZE_MAX;
if (impl->md == NULL) {
KDFerr(KDF_F_KDF_HKDF_SIZE, KDF_R_MISSING_MESSAGE_DIGEST);
return 0;
}
sz = EVP_MD_size(impl->md);
if (sz < 0)
return 0;
return sz;
}
static int kdf_hkdf_derive(EVP_KDF_IMPL *impl, unsigned char *key,
size_t keylen)
{
if (impl->md == NULL) {
KDFerr(KDF_F_KDF_HKDF_DERIVE, KDF_R_MISSING_MESSAGE_DIGEST);
return 0;
}
if (impl->key == NULL) {
KDFerr(KDF_F_KDF_HKDF_DERIVE, KDF_R_MISSING_KEY);
return 0;
}
switch (impl->mode) {
case EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND:
return HKDF(impl->md, impl->salt, impl->salt_len, impl->key,
impl->key_len, impl->info, impl->info_len, key,
keylen);
case EVP_KDF_HKDF_MODE_EXTRACT_ONLY:
return HKDF_Extract(impl->md, impl->salt, impl->salt_len, impl->key,
impl->key_len, key, keylen);
case EVP_KDF_HKDF_MODE_EXPAND_ONLY:
return HKDF_Expand(impl->md, impl->key, impl->key_len, impl->info,
impl->info_len, key, keylen);
default:
return 0;
}
}
const EVP_KDF hkdf_kdf_meth = {
EVP_KDF_HKDF,
kdf_hkdf_new,
kdf_hkdf_free,
kdf_hkdf_reset,
kdf_hkdf_ctrl,
kdf_hkdf_ctrl_str,
kdf_hkdf_size,
kdf_hkdf_derive
};
/*
* 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) {
KDFerr(KDF_F_HKDF_EXTRACT, KDF_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;
}
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