openssl/crypto/rand/drbg_ctr.c

/*
 * Copyright 2011-2018 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (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 <string.h>
#include <openssl/crypto.h>
#include <openssl/err.h>
#include <openssl/rand.h>
#include "rand_lcl.h"
#include "internal/thread_once.h"

/*
 * Implementation of NIST SP 800-90A CTR DRBG.
 */

static void inc_128(RAND_DRBG_CTR *ctr)
{
    int i;
    unsigned char c;
    unsigned char *p = &ctr->V[15];

    for (i = 0; i < 16; i++, p--) {
        c = *p;
        c++;
        *p = c;
        if (c != 0) {
            /* If we didn't wrap around, we're done. */
            break;
        }
    }
}

static void ctr_XOR(RAND_DRBG_CTR *ctr, const unsigned char *in, size_t inlen)
{
    size_t i, n;

    if (in == NULL || inlen == 0)
        return;

    /*
     * Any zero padding will have no effect on the result as we
     * are XORing. So just process however much input we have.
     */
    n = inlen < ctr->keylen ? inlen : ctr->keylen;
    for (i = 0; i < n; i++)
        ctr->K[i] ^= in[i];
    if (inlen <= ctr->keylen)
        return;

    n = inlen - ctr->keylen;
    if (n > 16) {
        /* Should never happen */
        n = 16;
    }
    for (i = 0; i < n; i++)
        ctr->V[i] ^= in[i + ctr->keylen];
}

/*
 * Process a complete block using BCC algorithm of SP 800-90A 10.3.3
 */
static void ctr_BCC_block(RAND_DRBG_CTR *ctr, unsigned char *out,
                          const unsigned char *in)
{
    int i;

    for (i = 0; i < 16; i++)
        out[i] ^= in[i];
    AES_encrypt(out, out, &ctr->df_ks);
}


/*
 * Handle several BCC operations for as much data as we need for K and X
 */
static void ctr_BCC_blocks(RAND_DRBG_CTR *ctr, const unsigned char *in)
{
    ctr_BCC_block(ctr, ctr->KX, in);
    ctr_BCC_block(ctr, ctr->KX + 16, in);
    if (ctr->keylen != 16)
        ctr_BCC_block(ctr, ctr->KX + 32, in);
}

/*
 * Initialise BCC blocks: these have the value 0,1,2 in leftmost positions:
 * see 10.3.1 stage 7.
 */
static void ctr_BCC_init(RAND_DRBG_CTR *ctr)
{
    memset(ctr->KX, 0, 48);
    memset(ctr->bltmp, 0, 16);
    ctr_BCC_block(ctr, ctr->KX, ctr->bltmp);
    ctr->bltmp[3] = 1;
    ctr_BCC_block(ctr, ctr->KX + 16, ctr->bltmp);
    if (ctr->keylen != 16) {
        ctr->bltmp[3] = 2;
        ctr_BCC_block(ctr, ctr->KX + 32, ctr->bltmp);
    }
}

/*
 * Process several blocks into BCC algorithm, some possibly partial
 */
static void ctr_BCC_update(RAND_DRBG_CTR *ctr,
                           const unsigned char *in, size_t inlen)
{
    if (in == NULL || inlen == 0)
        return;

    /* If we have partial block handle it first */
    if (ctr->bltmp_pos) {
        size_t left = 16 - ctr->bltmp_pos;

        /* If we now have a complete block process it */
        if (inlen >= left) {
            memcpy(ctr->bltmp + ctr->bltmp_pos, in, left);
            ctr_BCC_blocks(ctr, ctr->bltmp);
            ctr->bltmp_pos = 0;
            inlen -= left;
            in += left;
        }
    }

    /* Process zero or more complete blocks */
    for (; inlen >= 16; in += 16, inlen -= 16) {
        ctr_BCC_blocks(ctr, in);
    }

    /* Copy any remaining partial block to the temporary buffer */
    if (inlen > 0) {
        memcpy(ctr->bltmp + ctr->bltmp_pos, in, inlen);
        ctr->bltmp_pos += inlen;
    }
}

static void ctr_BCC_final(RAND_DRBG_CTR *ctr)
{
    if (ctr->bltmp_pos) {
        memset(ctr->bltmp + ctr->bltmp_pos, 0, 16 - ctr->bltmp_pos);
        ctr_BCC_blocks(ctr, ctr->bltmp);
    }
}

static void ctr_df(RAND_DRBG_CTR *ctr,
                   const unsigned char *in1, size_t in1len,
                   const unsigned char *in2, size_t in2len,
                   const unsigned char *in3, size_t in3len)
{
    static unsigned char c80 = 0x80;
    size_t inlen;
    unsigned char *p = ctr->bltmp;

    ctr_BCC_init(ctr);
    if (in1 == NULL)
        in1len = 0;
    if (in2 == NULL)
        in2len = 0;
    if (in3 == NULL)
        in3len = 0;
    inlen = in1len + in2len + in3len;
    /* Initialise L||N in temporary block */
    *p++ = (inlen >> 24) & 0xff;
    *p++ = (inlen >> 16) & 0xff;
    *p++ = (inlen >> 8) & 0xff;
    *p++ = inlen & 0xff;

    /* NB keylen is at most 32 bytes */
    *p++ = 0;
    *p++ = 0;
    *p++ = 0;
    *p = (unsigned char)((ctr->keylen + 16) & 0xff);
    ctr->bltmp_pos = 8;
    ctr_BCC_update(ctr, in1, in1len);
    ctr_BCC_update(ctr, in2, in2len);
    ctr_BCC_update(ctr, in3, in3len);
    ctr_BCC_update(ctr, &c80, 1);
    ctr_BCC_final(ctr);
    /* Set up key K */
    AES_set_encrypt_key(ctr->KX, ctr->keylen * 8, &ctr->df_kxks);
    /* X follows key K */
    AES_encrypt(ctr->KX + ctr->keylen, ctr->KX, &ctr->df_kxks);
    AES_encrypt(ctr->KX, ctr->KX + 16, &ctr->df_kxks);
    if (ctr->keylen != 16)
        AES_encrypt(ctr->KX + 16, ctr->KX + 32, &ctr->df_kxks);
}

/*
 * NB the no-df Update in SP800-90A specifies a constant input length
 * of seedlen, however other uses of this algorithm pad the input with
 * zeroes if necessary and have up to two parameters XORed together,
 * so we handle both cases in this function instead.
 */
static void ctr_update(RAND_DRBG *drbg,
                       const unsigned char *in1, size_t in1len,
                       const unsigned char *in2, size_t in2len,
                       const unsigned char *nonce, size_t noncelen)
{
    RAND_DRBG_CTR *ctr = &drbg->data.ctr;

    /* ks is already setup for correct key */
    inc_128(ctr);
    AES_encrypt(ctr->V, ctr->K, &ctr->ks);

    /* If keylen longer than 128 bits need extra encrypt */
    if (ctr->keylen != 16) {
        inc_128(ctr);
        AES_encrypt(ctr->V, ctr->K + 16, &ctr->ks);
    }
    inc_128(ctr);
    AES_encrypt(ctr->V, ctr->V, &ctr->ks);

    /* If 192 bit key part of V is on end of K */
    if (ctr->keylen == 24) {
        memcpy(ctr->V + 8, ctr->V, 8);
        memcpy(ctr->V, ctr->K + 24, 8);
    }

    if (drbg->flags & RAND_DRBG_FLAG_CTR_USE_DF) {
        /* If no input reuse existing derived value */
        if (in1 != NULL || nonce != NULL || in2 != NULL)
            ctr_df(ctr, in1, in1len, nonce, noncelen, in2, in2len);
        /* If this a reuse input in1len != 0 */
        if (in1len)
            ctr_XOR(ctr, ctr->KX, drbg->seedlen);
    } else {
        ctr_XOR(ctr, in1, in1len);
        ctr_XOR(ctr, in2, in2len);
    }

    AES_set_encrypt_key(ctr->K, drbg->strength, &ctr->ks);
}

static int drbg_ctr_instantiate(RAND_DRBG *drbg,
                                const unsigned char *entropy, size_t entropylen,
                                const unsigned char *nonce, size_t noncelen,
                                const unsigned char *pers, size_t perslen)
{
    RAND_DRBG_CTR *ctr = &drbg->data.ctr;

    if (entropy == NULL)
        return 0;

    memset(ctr->K, 0, sizeof(ctr->K));
    memset(ctr->V, 0, sizeof(ctr->V));
    AES_set_encrypt_key(ctr->K, drbg->strength, &ctr->ks);
    ctr_update(drbg, entropy, entropylen, pers, perslen, nonce, noncelen);
    return 1;
}

static int drbg_ctr_reseed(RAND_DRBG *drbg,
                           const unsigned char *entropy, size_t entropylen,
                           const unsigned char *adin, size_t adinlen)
{
    if (entropy == NULL)
        return 0;
    ctr_update(drbg, entropy, entropylen, adin, adinlen, NULL, 0);
    return 1;
}

static int drbg_ctr_generate(RAND_DRBG *drbg,
                             unsigned char *out, size_t outlen,
                             const unsigned char *adin, size_t adinlen)
{
    RAND_DRBG_CTR *ctr = &drbg->data.ctr;

    if (adin != NULL && adinlen != 0) {
        ctr_update(drbg, adin, adinlen, NULL, 0, NULL, 0);
        /* This means we reuse derived value */
        if (drbg->flags & RAND_DRBG_FLAG_CTR_USE_DF) {
            adin = NULL;
            adinlen = 1;
        }
    } else {
        adinlen = 0;
    }

    for ( ; ; ) {
        inc_128(ctr);
        if (outlen < 16) {
            /* Use K as temp space as it will be updated */
            AES_encrypt(ctr->V, ctr->K, &ctr->ks);
            memcpy(out, ctr->K, outlen);
            break;
        }
        AES_encrypt(ctr->V, out, &ctr->ks);
        out += 16;
        outlen -= 16;
        if (outlen == 0)
            break;
    }

    ctr_update(drbg, adin, adinlen, NULL, 0, NULL, 0);
    return 1;
}

static int drbg_ctr_uninstantiate(RAND_DRBG *drbg)
{
    OPENSSL_cleanse(&drbg->data.ctr, sizeof(drbg->data.ctr));
    return 1;
}

static RAND_DRBG_METHOD drbg_ctr_meth = {
    drbg_ctr_instantiate,
    drbg_ctr_reseed,
    drbg_ctr_generate,
    drbg_ctr_uninstantiate
};

int drbg_ctr_init(RAND_DRBG *drbg)
{
    RAND_DRBG_CTR *ctr = &drbg->data.ctr;
    size_t keylen;

    switch (drbg->nid) {
    default:
        /* This can't happen, but silence the compiler warning. */
        return 0;
    case NID_aes_128_ctr:
        keylen = 16;
        break;
    case NID_aes_192_ctr:
        keylen = 24;
        break;
    case NID_aes_256_ctr:
        keylen = 32;
        break;
    }

    drbg->meth = &drbg_ctr_meth;

    ctr->keylen = keylen;
    drbg->strength = keylen * 8;
    drbg->seedlen = keylen + 16;

    if (drbg->flags & RAND_DRBG_FLAG_CTR_USE_DF) {
        /* df initialisation */
        static unsigned char df_key[32] = {
            0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,
            0x08,0x09,0x0a,0x0b,0x0c,0x0d,0x0e,0x0f,
            0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,
            0x18,0x19,0x1a,0x1b,0x1c,0x1d,0x1e,0x1f
        };
        /* Set key schedule for df_key */
        AES_set_encrypt_key(df_key, drbg->strength, &ctr->df_ks);

        drbg->min_entropylen = ctr->keylen;
        drbg->max_entropylen = DRBG_MINMAX_FACTOR * drbg->min_entropylen;
        drbg->min_noncelen = drbg->min_entropylen / 2;
        drbg->max_noncelen = DRBG_MINMAX_FACTOR * drbg->min_noncelen;
        drbg->max_perslen = DRBG_MAX_LENGTH;
        drbg->max_adinlen = DRBG_MAX_LENGTH;
    } else {
        drbg->min_entropylen = drbg->seedlen;
        drbg->max_entropylen = drbg->seedlen;
        /* Nonce not used */
        drbg->min_noncelen = 0;
        drbg->max_noncelen = 0;
        drbg->max_perslen = drbg->seedlen;
        drbg->max_adinlen = drbg->seedlen;
    }

    drbg->max_request = 1 << 16;
    drbg->reseed_interval = MAX_RESEED_INTERVAL;
    return 1;
}