pkcs5.c

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/*
 * PKCS #5 (Password-based Encryption)
 * Copyright (c) 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 "crypto/crypto.h"
#include "crypto/md5.h"
#include "asn1.h"
#include "pkcs5.h"


struct pkcs5_params {
        enum pkcs5_alg {
                PKCS5_ALG_UNKNOWN,
                PKCS5_ALG_MD5_DES_CBC
        } alg;
        u8 salt[8];
        size_t salt_len;
        unsigned int iter_count;
};


enum pkcs5_alg pkcs5_get_alg(struct asn1_oid *oid)
{
        if (oid->len == 7 &&
            oid->oid[0] == 1 /* iso */ &&
            oid->oid[1] == 2 /* member-body */ &&
            oid->oid[2] == 840 /* us */ &&
            oid->oid[3] == 113549 /* rsadsi */ &&
            oid->oid[4] == 1 /* pkcs */ &&
            oid->oid[5] == 5 /* pkcs-5 */ &&
            oid->oid[6] == 3 /* pbeWithMD5AndDES-CBC */)
                return PKCS5_ALG_MD5_DES_CBC;

        return PKCS5_ALG_UNKNOWN;
}


static int pkcs5_get_params(const u8 *enc_alg, size_t enc_alg_len,
                            struct pkcs5_params *params)
{
        struct asn1_hdr hdr;
        const u8 *enc_alg_end, *pos, *end;
        struct asn1_oid oid;
        char obuf[80];

        /* AlgorithmIdentifier */

        enc_alg_end = enc_alg + enc_alg_len;

        os_memset(params, 0, sizeof(*params));

        if (asn1_get_oid(enc_alg, enc_alg_end - enc_alg, &oid, &pos)) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Failed to parse OID "
                           "(algorithm)");
                return -1;
        }

        asn1_oid_to_str(&oid, obuf, sizeof(obuf));
        wpa_printf(MSG_DEBUG, "PKCS #5: encryption algorithm %s", obuf);
        params->alg = pkcs5_get_alg(&oid);
        if (params->alg == PKCS5_ALG_UNKNOWN) {
                wpa_printf(MSG_INFO, "PKCS #5: unsupported encryption "
                           "algorithm %s", obuf);
                return -1;
        }

        /*
         * PKCS#5, Section 8
         * PBEParameter ::= SEQUENCE {
         *   salt OCTET STRING SIZE(8),
         *   iterationCount INTEGER }
         */

        if (asn1_get_next(pos, enc_alg_end - pos, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL ||
            hdr.tag != ASN1_TAG_SEQUENCE) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Expected SEQUENCE "
                           "(PBEParameter) - found class %d tag 0x%x",
                           hdr.class, hdr.tag);
                return -1;
        }
        pos = hdr.payload;
        end = hdr.payload + hdr.length;

        /* salt OCTET STRING SIZE(8) */
        if (asn1_get_next(pos, end - pos, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL ||
            hdr.tag != ASN1_TAG_OCTETSTRING ||
            hdr.length != 8) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Expected OCTETSTRING SIZE(8) "
                           "(salt) - found class %d tag 0x%x size %d",
                           hdr.class, hdr.tag, hdr.length);
                return -1;
        }
        pos = hdr.payload + hdr.length;
        os_memcpy(params->salt, hdr.payload, hdr.length);
        params->salt_len = hdr.length;
        wpa_hexdump(MSG_DEBUG, "PKCS #5: salt",
                    params->salt, params->salt_len);

        /* iterationCount INTEGER */
        if (asn1_get_next(pos, end - pos, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL || hdr.tag != ASN1_TAG_INTEGER) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Expected INTEGER - found "
                           "class %d tag 0x%x", hdr.class, hdr.tag);
                return -1;
        }
        if (hdr.length == 1)
                params->iter_count = *hdr.payload;
        else if (hdr.length == 2)
                params->iter_count = WPA_GET_BE16(hdr.payload);
        else if (hdr.length == 4)
                params->iter_count = WPA_GET_BE32(hdr.payload);
        else {
                wpa_hexdump(MSG_DEBUG, "PKCS #5: Unsupported INTEGER value "
                            " (iterationCount)",
                            hdr.payload, hdr.length);
                return -1;
        }
        wpa_printf(MSG_DEBUG, "PKCS #5: iterationCount=0x%x",
                   params->iter_count);
        if (params->iter_count == 0 || params->iter_count > 0xffff) {
                wpa_printf(MSG_INFO, "PKCS #5: Unsupported "
                           "iterationCount=0x%x", params->iter_count);
                return -1;
        }

        return 0;
}


static struct crypto_cipher * pkcs5_crypto_init(struct pkcs5_params *params,
                                                const char *passwd)
{
        unsigned int i;
        u8 hash[MD5_MAC_LEN];
        const u8 *addr[2];
        size_t len[2];

        if (params->alg != PKCS5_ALG_MD5_DES_CBC)
                return NULL;

        addr[0] = (const u8 *) passwd;
        len[0] = os_strlen(passwd);
        addr[1] = params->salt;
        len[1] = params->salt_len;
        if (md5_vector(2, addr, len, hash) < 0)
                return NULL;
        addr[0] = hash;
        len[0] = MD5_MAC_LEN;
        for (i = 1; i < params->iter_count; i++) {
                if (md5_vector(1, addr, len, hash) < 0)
                        return NULL;
        }
        /* TODO: DES key parity bits(?) */
        wpa_hexdump_key(MSG_DEBUG, "PKCS #5: DES key", hash, 8);
        wpa_hexdump_key(MSG_DEBUG, "PKCS #5: DES IV", hash + 8, 8);

        return crypto_cipher_init(CRYPTO_CIPHER_ALG_DES, hash + 8, hash, 8);
}


u8 * pkcs5_decrypt(const u8 *enc_alg, size_t enc_alg_len,
                   const u8 *enc_data, size_t enc_data_len,
                   const char *passwd, size_t *data_len)
{
        struct crypto_cipher *ctx;
        u8 *eb, pad;
        struct pkcs5_params params;
        unsigned int i;

        if (pkcs5_get_params(enc_alg, enc_alg_len, &params) < 0) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Unsupported parameters");
                return NULL;
        }

        ctx = pkcs5_crypto_init(&params, passwd);
        if (ctx == NULL) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Failed to initialize crypto");
                return NULL;
        }

        /* PKCS #5, Section 7 - Decryption process */
        if (enc_data_len < 16 || enc_data_len % 8) {
                wpa_printf(MSG_INFO, "PKCS #5: invalid length of ciphertext "
                           "%d", (int) enc_data_len);
                crypto_cipher_deinit(ctx);
                return NULL;
        }

        eb = os_malloc(enc_data_len);
        if (eb == NULL) {
                crypto_cipher_deinit(ctx);
                return NULL;
        }

        if (crypto_cipher_decrypt(ctx, enc_data, eb, enc_data_len) < 0) {
                wpa_printf(MSG_DEBUG, "PKCS #5: Failed to decrypt EB");
                crypto_cipher_deinit(ctx);
                os_free(eb);
                return NULL;
        }
        crypto_cipher_deinit(ctx);

        pad = eb[enc_data_len - 1];
        if (pad > 8) {
                wpa_printf(MSG_INFO, "PKCS #5: Invalid PS octet 0x%x", pad);
                os_free(eb);
                return NULL;
        }
        for (i = enc_data_len - pad; i < enc_data_len; i++) {
                if (eb[i] != pad) {
                        wpa_hexdump(MSG_INFO, "PKCS #5: Invalid PS",
                                    eb + enc_data_len - pad, pad);
                        os_free(eb);
                        return NULL;
                }
        }

        wpa_hexdump_key(MSG_MSGDUMP, "PKCS #5: message M (encrypted key)",
                        eb, enc_data_len - pad);

        *data_len = enc_data_len - pad;
        return eb;
}