pkcs1.c

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/*
 * PKCS #1 (RSA Encryption)
 * Copyright (c) 2006-2009, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */

#include "includes.h"

#include "common.h"
#include "rsa.h"
#include "pkcs1.h"


static int pkcs1_generate_encryption_block(u8 block_type, size_t modlen,
                                           const u8 *in, size_t inlen,
                                           u8 *out, size_t *outlen)
{
        size_t ps_len;
        u8 *pos;

        /*
         * PKCS #1 v1.5, 8.1:
         *
         * EB = 00 || BT || PS || 00 || D
         * BT = 00 or 01 for private-key operation; 02 for public-key operation
         * PS = k-3-||D||; at least eight octets
         * (BT=0: PS=0x00, BT=1: PS=0xff, BT=2: PS=pseudorandom non-zero)
         * k = length of modulus in octets (modlen)
         */

        if (modlen < 12 || modlen > *outlen || inlen > modlen - 11) {
                wpa_printf(MSG_DEBUG, "PKCS #1: %s - Invalid buffer "
                           "lengths (modlen=%lu outlen=%lu inlen=%lu)",
                           __func__, (unsigned long) modlen,
                           (unsigned long) *outlen,
                           (unsigned long) inlen);
                return -1;
        }

        pos = out;
        *pos++ = 0x00;
        *pos++ = block_type; /* BT */
        ps_len = modlen - inlen - 3;
        switch (block_type) {
        case 0:
                os_memset(pos, 0x00, ps_len);
                pos += ps_len;
                break;
        case 1:
                os_memset(pos, 0xff, ps_len);
                pos += ps_len;
                break;
        case 2:
                if (os_get_random(pos, ps_len) < 0) {
                        wpa_printf(MSG_DEBUG, "PKCS #1: %s - Failed to get "
                                   "random data for PS", __func__);
                        return -1;
                }
                while (ps_len--) {
                        if (*pos == 0x00)
                                *pos = 0x01;
                        pos++;
                }
                break;
        default:
                wpa_printf(MSG_DEBUG, "PKCS #1: %s - Unsupported block type "
                           "%d", __func__, block_type);
                return -1;
        }
        *pos++ = 0x00;
        os_memcpy(pos, in, inlen); /* D */

        return 0;
}


int pkcs1_encrypt(int block_type, struct crypto_rsa_key *key,
                  int use_private, const u8 *in, size_t inlen,
                  u8 *out, size_t *outlen)
{
        size_t modlen;

        modlen = crypto_rsa_get_modulus_len(key);

        if (pkcs1_generate_encryption_block(block_type, modlen, in, inlen,
                                            out, outlen) < 0)
                return -1;

        return crypto_rsa_exptmod(out, modlen, out, outlen, key, use_private);
}


int pkcs1_v15_private_key_decrypt(struct crypto_rsa_key *key,
                                  const u8 *in, size_t inlen,
                                  u8 *out, size_t *outlen)
{
        int res;
        u8 *pos, *end;

        res = crypto_rsa_exptmod(in, inlen, out, outlen, key, 1);
        if (res)
                return res;

        if (*outlen < 2 || out[0] != 0 || out[1] != 2)
                return -1;

        /* Skip PS (pseudorandom non-zero octets) */
        pos = out + 2;
        end = out + *outlen;
        while (*pos && pos < end)
                pos++;
        if (pos == end)
                return -1;
        pos++;

        *outlen -= pos - out;

        /* Strip PKCS #1 header */
        os_memmove(out, pos, *outlen);

        return 0;
}


int pkcs1_decrypt_public_key(struct crypto_rsa_key *key,
                             const u8 *crypt, size_t crypt_len,
                             u8 *plain, size_t *plain_len)
{
        size_t len;
        u8 *pos;

        len = *plain_len;
        if (crypto_rsa_exptmod(crypt, crypt_len, plain, &len, key, 0) < 0)
                return -1;

        /*
         * PKCS #1 v1.5, 8.1:
         *
         * EB = 00 || BT || PS || 00 || D
         * BT = 00 or 01
         * PS = k-3-||D|| times (00 if BT=00) or (FF if BT=01)
         * k = length of modulus in octets
         */

        if (len < 3 + 8 + 16 /* min hash len */ ||
            plain[0] != 0x00 || (plain[1] != 0x00 && plain[1] != 0x01)) {
                wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature EB "
                           "structure");
                return -1;
        }

        pos = plain + 3;
        if (plain[1] == 0x00) {
                /* BT = 00 */
                if (plain[2] != 0x00) {
                        wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature "
                                   "PS (BT=00)");
                        return -1;
                }
                while (pos + 1 < plain + len && *pos == 0x00 && pos[1] == 0x00)
                        pos++;
        } else {
                /* BT = 01 */
                if (plain[2] != 0xff) {
                        wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature "
                                   "PS (BT=01)");
                        return -1;
                }
                while (pos < plain + len && *pos == 0xff)
                        pos++;
        }

        if (pos - plain - 2 < 8) {
                /* PKCS #1 v1.5, 8.1: At least eight octets long PS */
                wpa_printf(MSG_INFO, "LibTomCrypt: Too short signature "
                           "padding");
                return -1;
        }

        if (pos + 16 /* min hash len */ >= plain + len || *pos != 0x00) {
                wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature EB "
                           "structure (2)");
                return -1;
        }
        pos++;
        len -= pos - plain;

        /* Strip PKCS #1 header */
        os_memmove(plain, pos, len);
        *plain_len = len;

        return 0;
}