/* * Copyright (C) 2011 Nokia Corporation * Copyright (C) 2011 Intel Corporation * * Author: * Dmitry Kasatkin <dmitry.kasatkin@nokia.com> * <dmitry.kasatkin@intel.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, version 2 of the License. * * File: sign.c * implements signature (RSA) verification * pkcs decoding is based on LibTomCrypt code */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/err.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/key.h> #include <linux/crypto.h> #include <crypto/hash.h> #include <crypto/sha.h> #include <keys/user-type.h> #include <linux/mpi.h> #include <linux/digsig.h> static struct crypto_shash *shash; static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg, unsigned long msglen, unsigned long modulus_bitlen, unsigned long *outlen) { unsigned long modulus_len, ps_len, i; modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); /* test message size */ if ((msglen > modulus_len) || (modulus_len < 11)) return NULL; /* separate encoded message */ if (msg[0] != 0x00 || msg[1] != 0x01) return NULL; for (i = 2; i < modulus_len - 1; i++) if (msg[i] != 0xFF) break; /* separator check */ if (msg[i] != 0) /* There was no octet with hexadecimal value 0x00 to separate ps from m. */ return NULL; ps_len = i - 2; *outlen = (msglen - (2 + ps_len + 1)); return msg + 2 + ps_len + 1; } /* * RSA Signature verification with public key */ static int digsig_verify_rsa(struct key *key, const char *sig, int siglen, const char *h, int hlen) { int err = -EINVAL; unsigned long len; unsigned long mlen, mblen; unsigned nret, l; int head, i; unsigned char *out1 = NULL; const char *m; MPI in = NULL, res = NULL, pkey[2]; uint8_t *p, *datap; const uint8_t *endp; const struct user_key_payload *ukp; struct pubkey_hdr *pkh; down_read(&key->sem); ukp = user_key_payload(key); if (ukp->datalen < sizeof(*pkh)) goto err1; pkh = (struct pubkey_hdr *)ukp->data; if (pkh->version != 1) goto err1; if (pkh->algo != PUBKEY_ALGO_RSA) goto err1; if (pkh->nmpi != 2) goto err1; datap = pkh->mpi; endp = ukp->data + ukp->datalen; err = -ENOMEM; for (i = 0; i < pkh->nmpi; i++) { unsigned int remaining = endp - datap; pkey[i] = mpi_read_from_buffer(datap, &remaining); if (!pkey[i]) goto err; datap += remaining; } mblen = mpi_get_nbits(pkey[0]); mlen = DIV_ROUND_UP(mblen, 8); if (mlen == 0) goto err; out1 = kzalloc(mlen, GFP_KERNEL); if (!out1) goto err; nret = siglen; in = mpi_read_from_buffer(sig, &nret); if (!in) goto err; res = mpi_alloc(mpi_get_nlimbs(in) * 2); if (!res) goto err; err = mpi_powm(res, in, pkey[1], pkey[0]); if (err) goto err; if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) { err = -EINVAL; goto err; } p = mpi_get_buffer(res, &l, NULL); if (!p) { err = -EINVAL; goto err; } len = mlen; head = len - l; memset(out1, 0, head); memcpy(out1 + head, p, l); kfree(p); m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len); if (!m || len != hlen || memcmp(m, h, hlen)) err = -EINVAL; err: mpi_free(in); mpi_free(res); kfree(out1); while (--i >= 0) mpi_free(pkey[i]); err1: up_read(&key->sem); return err; } /** * digsig_verify() - digital signature verification with public key * @keyring: keyring to search key in * @sig: digital signature * @siglen: length of the signature * @data: data * @datalen: length of the data * * Returns 0 on success, -EINVAL otherwise * * Verifies data integrity against digital signature. * Currently only RSA is supported. * Normally hash of the content is used as a data for this function. * */ int digsig_verify(struct key *keyring, const char *sig, int siglen, const char *data, int datalen) { int err = -ENOMEM; struct signature_hdr *sh = (struct signature_hdr *)sig; struct shash_desc *desc = NULL; unsigned char hash[SHA1_DIGEST_SIZE]; struct key *key; char name[20]; if (siglen < sizeof(*sh) + 2) return -EINVAL; if (sh->algo != PUBKEY_ALGO_RSA) return -ENOTSUPP; sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid)); if (keyring) { /* search in specific keyring */ key_ref_t kref; kref = keyring_search(make_key_ref(keyring, 1UL), &key_type_user, name); if (IS_ERR(kref)) key = ERR_CAST(kref); else key = key_ref_to_ptr(kref); } else { key = request_key(&key_type_user, name, NULL); } if (IS_ERR(key)) { pr_err("key not found, id: %s\n", name); return PTR_ERR(key); } desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash), GFP_KERNEL); if (!desc) goto err; desc->tfm = shash; desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; crypto_shash_init(desc); crypto_shash_update(desc, data, datalen); crypto_shash_update(desc, sig, sizeof(*sh)); crypto_shash_final(desc, hash); kfree(desc); /* pass signature mpis address */ err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh), hash, sizeof(hash)); err: key_put(key); return err ? -EINVAL : 0; } EXPORT_SYMBOL_GPL(digsig_verify); static int __init digsig_init(void) { shash = crypto_alloc_shash("sha1", 0, 0); if (IS_ERR(shash)) { pr_err("shash allocation failed\n"); return PTR_ERR(shash); } return 0; } static void __exit digsig_cleanup(void) { crypto_free_shash(shash); } module_init(digsig_init); module_exit(digsig_cleanup); MODULE_LICENSE("GPL");