linux/lib/digsig.c
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   1/*
   2 * Copyright (C) 2011 Nokia Corporation
   3 * Copyright (C) 2011 Intel Corporation
   4 *
   5 * Author:
   6 * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
   7 *                 <dmitry.kasatkin@intel.com>
   8 *
   9 * This program is free software; you can redistribute it and/or modify
  10 * it under the terms of the GNU General Public License as published by
  11 * the Free Software Foundation, version 2 of the License.
  12 *
  13 * File: sign.c
  14 *      implements signature (RSA) verification
  15 *      pkcs decoding is based on LibTomCrypt code
  16 */
  17
  18#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  19
  20#include <linux/err.h>
  21#include <linux/module.h>
  22#include <linux/slab.h>
  23#include <linux/key.h>
  24#include <linux/crypto.h>
  25#include <crypto/hash.h>
  26#include <crypto/sha.h>
  27#include <keys/user-type.h>
  28#include <linux/mpi.h>
  29#include <linux/digsig.h>
  30
  31static struct crypto_shash *shash;
  32
  33static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
  34                                                unsigned long  msglen,
  35                                                unsigned long  modulus_bitlen,
  36                                                unsigned long *outlen)
  37{
  38        unsigned long modulus_len, ps_len, i;
  39
  40        modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
  41
  42        /* test message size */
  43        if ((msglen > modulus_len) || (modulus_len < 11))
  44                return NULL;
  45
  46        /* separate encoded message */
  47        if (msg[0] != 0x00 || msg[1] != 0x01)
  48                return NULL;
  49
  50        for (i = 2; i < modulus_len - 1; i++)
  51                if (msg[i] != 0xFF)
  52                        break;
  53
  54        /* separator check */
  55        if (msg[i] != 0)
  56                /* There was no octet with hexadecimal value 0x00
  57                to separate ps from m. */
  58                return NULL;
  59
  60        ps_len = i - 2;
  61
  62        *outlen = (msglen - (2 + ps_len + 1));
  63
  64        return msg + 2 + ps_len + 1;
  65}
  66
  67/*
  68 * RSA Signature verification with public key
  69 */
  70static int digsig_verify_rsa(struct key *key,
  71                    const char *sig, int siglen,
  72                       const char *h, int hlen)
  73{
  74        int err = -EINVAL;
  75        unsigned long len;
  76        unsigned long mlen, mblen;
  77        unsigned nret, l;
  78        int head, i;
  79        unsigned char *out1 = NULL;
  80        const char *m;
  81        MPI in = NULL, res = NULL, pkey[2];
  82        uint8_t *p, *datap, *endp;
  83        struct user_key_payload *ukp;
  84        struct pubkey_hdr *pkh;
  85
  86        down_read(&key->sem);
  87        ukp = key->payload.data;
  88
  89        if (ukp->datalen < sizeof(*pkh))
  90                goto err1;
  91
  92        pkh = (struct pubkey_hdr *)ukp->data;
  93
  94        if (pkh->version != 1)
  95                goto err1;
  96
  97        if (pkh->algo != PUBKEY_ALGO_RSA)
  98                goto err1;
  99
 100        if (pkh->nmpi != 2)
 101                goto err1;
 102
 103        datap = pkh->mpi;
 104        endp = ukp->data + ukp->datalen;
 105
 106        err = -ENOMEM;
 107
 108        for (i = 0; i < pkh->nmpi; i++) {
 109                unsigned int remaining = endp - datap;
 110                pkey[i] = mpi_read_from_buffer(datap, &remaining);
 111                if (!pkey[i])
 112                        goto err;
 113                datap += remaining;
 114        }
 115
 116        mblen = mpi_get_nbits(pkey[0]);
 117        mlen = DIV_ROUND_UP(mblen, 8);
 118
 119        if (mlen == 0)
 120                goto err;
 121
 122        out1 = kzalloc(mlen, GFP_KERNEL);
 123        if (!out1)
 124                goto err;
 125
 126        nret = siglen;
 127        in = mpi_read_from_buffer(sig, &nret);
 128        if (!in)
 129                goto err;
 130
 131        res = mpi_alloc(mpi_get_nlimbs(in) * 2);
 132        if (!res)
 133                goto err;
 134
 135        err = mpi_powm(res, in, pkey[1], pkey[0]);
 136        if (err)
 137                goto err;
 138
 139        if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
 140                err = -EINVAL;
 141                goto err;
 142        }
 143
 144        p = mpi_get_buffer(res, &l, NULL);
 145        if (!p) {
 146                err = -EINVAL;
 147                goto err;
 148        }
 149
 150        len = mlen;
 151        head = len - l;
 152        memset(out1, 0, head);
 153        memcpy(out1 + head, p, l);
 154
 155        kfree(p);
 156
 157        m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
 158
 159        if (!m || len != hlen || memcmp(m, h, hlen))
 160                err = -EINVAL;
 161
 162err:
 163        mpi_free(in);
 164        mpi_free(res);
 165        kfree(out1);
 166        while (--i >= 0)
 167                mpi_free(pkey[i]);
 168err1:
 169        up_read(&key->sem);
 170
 171        return err;
 172}
 173
 174/**
 175 * digsig_verify() - digital signature verification with public key
 176 * @keyring:    keyring to search key in
 177 * @sig:        digital signature
 178 * @sigen:      length of the signature
 179 * @data:       data
 180 * @datalen:    length of the data
 181 * @return:     0 on success, -EINVAL otherwise
 182 *
 183 * Verifies data integrity against digital signature.
 184 * Currently only RSA is supported.
 185 * Normally hash of the content is used as a data for this function.
 186 *
 187 */
 188int digsig_verify(struct key *keyring, const char *sig, int siglen,
 189                                                const char *data, int datalen)
 190{
 191        int err = -ENOMEM;
 192        struct signature_hdr *sh = (struct signature_hdr *)sig;
 193        struct shash_desc *desc = NULL;
 194        unsigned char hash[SHA1_DIGEST_SIZE];
 195        struct key *key;
 196        char name[20];
 197
 198        if (siglen < sizeof(*sh) + 2)
 199                return -EINVAL;
 200
 201        if (sh->algo != PUBKEY_ALGO_RSA)
 202                return -ENOTSUPP;
 203
 204        sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
 205
 206        if (keyring) {
 207                /* search in specific keyring */
 208                key_ref_t kref;
 209                kref = keyring_search(make_key_ref(keyring, 1UL),
 210                                                &key_type_user, name);
 211                if (IS_ERR(kref))
 212                        key = ERR_PTR(PTR_ERR(kref));
 213                else
 214                        key = key_ref_to_ptr(kref);
 215        } else {
 216                key = request_key(&key_type_user, name, NULL);
 217        }
 218        if (IS_ERR(key)) {
 219                pr_err("key not found, id: %s\n", name);
 220                return PTR_ERR(key);
 221        }
 222
 223        desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
 224                       GFP_KERNEL);
 225        if (!desc)
 226                goto err;
 227
 228        desc->tfm = shash;
 229        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 230
 231        crypto_shash_init(desc);
 232        crypto_shash_update(desc, data, datalen);
 233        crypto_shash_update(desc, sig, sizeof(*sh));
 234        crypto_shash_final(desc, hash);
 235
 236        kfree(desc);
 237
 238        /* pass signature mpis address */
 239        err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
 240                             hash, sizeof(hash));
 241
 242err:
 243        key_put(key);
 244
 245        return err ? -EINVAL : 0;
 246}
 247EXPORT_SYMBOL_GPL(digsig_verify);
 248
 249static int __init digsig_init(void)
 250{
 251        shash = crypto_alloc_shash("sha1", 0, 0);
 252        if (IS_ERR(shash)) {
 253                pr_err("shash allocation failed\n");
 254                return  PTR_ERR(shash);
 255        }
 256
 257        return 0;
 258
 259}
 260
 261static void __exit digsig_cleanup(void)
 262{
 263        crypto_free_shash(shash);
 264}
 265
 266module_init(digsig_init);
 267module_exit(digsig_cleanup);
 268
 269MODULE_LICENSE("GPL");
 270
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