hkdf.c

/**************************** hkdf.c ***************************/
/***************** See RFC 6234 for details. *******************/
/* Copyright (c) 2011 IETF Trust and the persons identified as */
/* authors of the code.  All rights reserved.                  */
/* See sha.h for terms of use and redistribution.              */

/*
 *  Description:
 *      This file implements the HKDF algorithm (HMAC-based
 *      Extract-and-Expand Key Derivation Function, RFC 5869),
 *      expressed in terms of the various SHA algorithms.
 */

#include <string.h>
#include <stdlib.h>

#include "sha.h"


/*
 *  hkdf
 *
 *  Description:
 *      This function will generate keying material using HKDF.
 *
 *  Parameters:
 *      whichSha: [in]
 *          One of SHA1, SHA224, SHA256, SHA384, SHA512
 *      salt[ ]: [in]
 *          The optional salt value (a non-secret random value);
 *          if not provided (salt == NULL), it is set internally
 *          to a string of HashLen(whichSha) zeros.
 *      salt_len: [in]
 *          The length of the salt value.  (Ignored if salt == NULL.)
 *      ikm[ ]: [in]
 *          Input keying material.
 *      ikm_len: [in]
 *          The length of the input keying material.
 *      info[ ]: [in]
 *          The optional context and application specific information.
 *          If info == NULL or a zero-length string, it is ignored.
 *      info_len: [in]
 *          The length of the optional context and application specific
 *          information.  (Ignored if info == NULL.)
 *      okm[ ]: [out]
 *          Where the HKDF is to be stored.
 *      okm_len: [in]
 *          The length of the buffer to hold okm.
 *          okm_len must be <= 255 * USHABlockSize(whichSha)
 *
 *  Notes:
 *      Calls hkdfExtract() and hkdfExpand().
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int hkdf(SHAversion whichSha,
    const unsigned char *salt, int salt_len,
    const unsigned char *ikm, int ikm_len,
    const unsigned char *info, int info_len,
    uint8_t okm[ ], int okm_len)
{
	uint8_t prk[USHAMaxHashSize];
	return hkdfExtract(whichSha, salt, salt_len, ikm, ikm_len, prk) ||
	    hkdfExpand(whichSha, prk, USHAHashSize(whichSha), info,
		info_len, okm, okm_len);
}

/*
 *  hkdfExtract
 *
 *  Description:
 *      This function will perform HKDF extraction.
 *
 *  Parameters:
 *      whichSha: [in]
 *          One of SHA1, SHA224, SHA256, SHA384, SHA512
 *      salt[ ]: [in]
 *          The optional salt value (a non-secret random value);
 *          if not provided (salt == NULL), it is set internally
 *          to a string of HashLen(whichSha) zeros.
 *      salt_len: [in]
 *          The length of the salt value.  (Ignored if salt == NULL.)
 *      ikm[ ]: [in]
 *          Input keying material.
 *      ikm_len: [in]
 *          The length of the input keying material.
 *      prk[ ]: [out]
 *          Array where the HKDF extraction is to be stored.
 *          Must be larger than USHAHashSize(whichSha);
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int hkdfExtract(SHAversion whichSha,
    const unsigned char *salt, int salt_len,
    const unsigned char *ikm, int ikm_len,
    uint8_t prk[USHAMaxHashSize])
{
	unsigned char nullSalt[USHAMaxHashSize];
	if (salt == 0) {
		salt = nullSalt;
		salt_len = USHAHashSize(whichSha);
		memset(nullSalt, '\0', (size_t)salt_len);
	} else if (salt_len < 0) {
		return shaBadParam;
	}
	return hmac(whichSha, ikm, ikm_len, salt, salt_len, prk);
}

/*
 *  hkdfExpand
 *
 *  Description:
 *      This function will perform HKDF expansion.
 *
 *  Parameters:
 *      whichSha: [in]
 *          One of SHA1, SHA224, SHA256, SHA384, SHA512
 *      prk[ ]: [in]
 *          The pseudo-random key to be expanded; either obtained
 *          directly from a cryptographically strong, uniformly
 *          distributed pseudo-random number generator, or as the
 *          output from hkdfExtract().
 *      prk_len: [in]
 *          The length of the pseudo-random key in prk;
 *          should at least be equal to USHAHashSize(whichSHA).
 *      info[ ]: [in]
 *          The optional context and application specific information.
 *          If info == NULL or a zero-length string, it is ignored.
 *      info_len: [in]
 *          The length of the optional context and application specific
 *          information.  (Ignored if info == NULL.)
 *      okm[ ]: [out]
 *          Where the HKDF is to be stored.
 *      okm_len: [in]
 *          The length of the buffer to hold okm.
 *          okm_len must be <= 255 * USHABlockSize(whichSha)
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int hkdfExpand(SHAversion whichSha, const uint8_t prk[ ], int prk_len,
    const unsigned char *info, int info_len,
    uint8_t okm[ ], int okm_len)
{
	int hash_len, N;
	unsigned char T[USHAMaxHashSize];
	int Tlen, where, i;

	if (info == 0) {
		info = (const unsigned char *)"";
		info_len = 0;
	} else if (info_len < 0) {
		return shaBadParam;
	}
	if (okm_len <= 0) return shaBadParam;
	if (!okm) return shaBadParam;

	hash_len = USHAHashSize(whichSha);
	if (prk_len < hash_len) return shaBadParam;
	N = okm_len / hash_len;
	if ((okm_len % hash_len) != 0) N++;
	if (N > 255) return shaBadParam;

	Tlen = 0;
	where = 0;
	for (i = 1; i <= N; i++) {
		HMACContext context;
		unsigned char c = (unsigned char)i;
		int ret = hmacReset(&context, whichSha, prk, prk_len) ||
		    hmacInput(&context, T, Tlen) ||
		    hmacInput(&context, info, info_len) ||
		    hmacInput(&context, &c, 1) ||
		    hmacResult(&context, T);
		if (ret != shaSuccess) return ret;
		memcpy(okm + where, T,
		    (i != N) ? (size_t)hash_len : (size_t)(okm_len - where));
		where += hash_len;
		Tlen = hash_len;
	}
	return shaSuccess;
}

/*
 *  hkdfReset
 *
 *  Description:
 *      This function will initialize the hkdfContext in preparation
 *      for key derivation using the modular HKDF interface for
 *      arbitrary length inputs.
 *
 *  Parameters:
 *      context: [in/out]
 *          The context to reset.
 *      whichSha: [in]
 *          One of SHA1, SHA224, SHA256, SHA384, SHA512
 *      salt[ ]: [in]
 *          The optional salt value (a non-secret random value);
 *          if not provided (salt == NULL), it is set internally
 *          to a string of HashLen(whichSha) zeros.
 *      salt_len: [in]
 *          The length of the salt value.  (Ignored if salt == NULL.)
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int hkdfReset(HKDFContext *context, enum SHAversion whichSha,
    const unsigned char *salt, int salt_len)
{
	unsigned char nullSalt[USHAMaxHashSize];
	if (!context) return shaNull;

	context->whichSha = whichSha;
	context->hashSize = USHAHashSize(whichSha);
	if (salt == 0) {
		salt = nullSalt;
		salt_len = context->hashSize;
		memset(nullSalt, '\0', (size_t)salt_len);
	}

	return hmacReset(&context->hmacContext, whichSha, salt, salt_len);
}

/*
 *  hkdfInput
 *
 *  Description:
 *      This function accepts an array of octets as the next portion
 *      of the input keying material.  It may be called multiple times.
 *
 *  Parameters:
 *      context: [in/out]
 *          The HKDF context to update.
 *      ikm[ ]: [in]
 *          An array of octets representing the next portion of
 *          the input keying material.
 *      ikm_len: [in]
 *          The length of ikm.
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int hkdfInput(HKDFContext *context, const unsigned char *ikm,
    int ikm_len)
{
	if (!context) return shaNull;
	if (context->Corrupted) return context->Corrupted;
	if (context->Computed) return context->Corrupted = shaStateError;
	return hmacInput(&context->hmacContext, ikm, ikm_len);
}

/*
 * hkdfFinalBits
 *
 * Description:
 *   This function will add in any final bits of the
 *   input keying material.
 *
 * Parameters:
 *   context: [in/out]
 *     The HKDF context to update
 *   ikm_bits: [in]
 *     The final bits of the input keying material, in the upper
 *     portion of the byte.  (Use 0b###00000 instead of 0b00000###
 *     to input the three bits ###.)
 *   ikm_bit_count: [in]
 *     The number of bits in message_bits, between 1 and 7.
 *
 * Returns:
 *   sha Error Code.
 */
int hkdfFinalBits(HKDFContext *context, uint8_t ikm_bits,
    unsigned int ikm_bit_count)
{
	if (!context) return shaNull;
	if (context->Corrupted) return context->Corrupted;
	if (context->Computed) return context->Corrupted = shaStateError;
	return hmacFinalBits(&context->hmacContext, ikm_bits, ikm_bit_count);
}

/*
 * hkdfResult
 *
 * Description:
 *   This function will finish the HKDF extraction and perform the
 *   final HKDF expansion.
 *
 * Parameters:
 *   context: [in/out]
 *     The HKDF context to use to calculate the HKDF hash.
 *   prk[ ]: [out]
 *     An optional location to store the HKDF extraction.
 *     Either NULL, or pointer to a buffer that must be
 *     larger than USHAHashSize(whichSha);
 *   info[ ]: [in]
 *     The optional context and application specific information.
 *     If info == NULL or a zero-length string, it is ignored.
 *   info_len: [in]
 *     The length of the optional context and application specific
 *     information.  (Ignored if info == NULL.)
 *   okm[ ]: [out]
 *     Where the HKDF is to be stored.
 *   okm_len: [in]
 *     The length of the buffer to hold okm.
 *     okm_len must be <= 255 * USHABlockSize(whichSha)
 *
 * Returns:
 *   sha Error Code.
 *
 */
int hkdfResult(HKDFContext *context,
    uint8_t prk[USHAMaxHashSize],
    const unsigned char *info, int info_len,
    uint8_t okm[ ], int okm_len)
{
	uint8_t prkbuf[USHAMaxHashSize];
	int ret;

	if (!context) return shaNull;
	if (context->Corrupted) return context->Corrupted;
	if (context->Computed) return context->Corrupted = shaStateError;
	if (!okm) return context->Corrupted = shaBadParam;
	if (!prk) prk = prkbuf;

	ret = hmacResult(&context->hmacContext, prk) ||
	    hkdfExpand((unsigned int)context->whichSha, prk, context->hashSize,
		info, info_len, okm, okm_len);
	context->Computed = 1;
	return context->Corrupted = ret;
}