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Subject[RFC v1.1 2/5] crypto: ksign - digital signature verification support
Date
From: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>

This patch implements RSA digital signature verification using GnuPG library.

Signature and public key have a special format and have special headers.
Signature header contains keyid, which is used to identify the key,
needed for signature verification.
Payload of the signature and the key are multi-precision integers.

Signing and key management utility "evmctl" is available on
http://meego.gitorious.org/meego-platform-security/evm-utils

Key is added to the kernel keyring with the name equal to a keyid.
evm-utils provide support to load PEM key into the keyring,
to convert PEM key to the kernel format and to load it into the keyring.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
---
crypto/Kconfig | 13 ++
crypto/Makefile | 3 +
crypto/ksign.c | 259 ++++++++++++++++++++++++++++++++++++++++++
include/linux/crypto/ksign.h | 48 ++++++++
4 files changed, 323 insertions(+), 0 deletions(-)
create mode 100644 crypto/ksign.c
create mode 100644 include/linux/crypto/ksign.h

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 4fb13ee..604b534 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -863,6 +863,19 @@ config CRYPTO_MPILIB
help
Multiprecision maths library from GnuPG

+config CRYPTO_KSIGN
+ bool "In-kernel signature checker (EXPERIMENTAL)"
+ depends on CRYPTO
+ help
+ Signature checker (used for module sig checking).
+
+config CRYPTO_KSIGN_RSA
+ bool "Handle RSA signatures (EXPERIMENTAL)"
+ select CRYPTO_KSIGN
+ select CRYPTO_MPILIB
+ help
+ RSA Signature checker.
+
source "drivers/crypto/Kconfig"

endif # if CRYPTO
diff --git a/crypto/Makefile b/crypto/Makefile
index 604006d..4ef05e8 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -90,6 +90,9 @@ obj-$(CONFIG_CRYPTO_USER_API_HASH) += algif_hash.o
obj-$(CONFIG_CRYPTO_USER_API_SKCIPHER) += algif_skcipher.o
obj-$(CONFIG_CRYPTO_MPILIB) += mpi/

+obj-$(CONFIG_CRYPTO_KSIGN) += ksignmod.o
+ksignmod-objs := ksign.o
+
#
# generic algorithms and the async_tx api
#
diff --git a/crypto/ksign.c b/crypto/ksign.c
new file mode 100644
index 0000000..60ccfc9
--- /dev/null
+++ b/crypto/ksign.c
@@ -0,0 +1,259 @@
+/*
+ * Copyright (C) 2011 Nokia Corporation
+ *
+ * Author:
+ * Dmitry Kasatkin <dmitry.kasatkin@nokia.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 originated from LibTomCrypt code
+ */
+
+#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/crypto/mpi.h>
+#include <linux/crypto/ksign.h>
+
+static struct crypto_shash *shash;
+
+static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
+ unsigned long msglen,
+ unsigned long modulus_bitlen,
+ unsigned char *out,
+ unsigned long *outlen,
+ int *is_valid)
+{
+ unsigned long modulus_len, ps_len, i;
+ int result;
+
+ /* default to invalid packet */
+ *is_valid = 0;
+
+ modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
+
+ /* test message size */
+ if ((msglen > modulus_len) || (modulus_len < 11))
+ return -EINVAL;
+
+ /* separate encoded message */
+ if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1)) {
+ result = -EINVAL;
+ goto bail;
+ }
+
+ 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. */
+ result = -EINVAL;
+ goto bail;
+ }
+
+ ps_len = i - 2;
+
+ if (*outlen < (msglen - (2 + ps_len + 1))) {
+ *outlen = msglen - (2 + ps_len + 1);
+ result = -EOVERFLOW;
+ goto bail;
+ }
+
+ *outlen = (msglen - (2 + ps_len + 1));
+ memcpy(out, &msg[2 + ps_len + 1], *outlen);
+
+ /* valid packet */
+ *is_valid = 1;
+ result = 0;
+bail:
+ return result;
+}
+
+/*
+ * RSA Signature verification with public key
+ */
+static int ksign_verify_rsa(struct key *key,
+ const char *sig, int siglen,
+ const char *h, int hlen)
+{
+ int err = -ENOMEM;
+ unsigned long len;
+ unsigned long mlen, mblen;
+ unsigned nret, l;
+ int valid, head, i;
+ unsigned char *out1 = NULL, *out2 = NULL;
+ MPI in = NULL, res = NULL, pkey[2];
+ uint8_t *p, *datap, *endp;
+ struct user_key_payload *ukp;
+ struct pubkey_hdr *pkh;
+
+ down_read(&key->sem);
+ ukp = key->payload.data;
+ pkh = (struct pubkey_hdr *)ukp->data;
+
+ if (pkh->version != 1)
+ return -EINVAL;
+
+ if (pkh->algo != PUBKEY_ALGO_RSA)
+ return -EINVAL;
+
+ if (pkh->nmpi != 2) {
+ err = -EINVAL;
+ goto err1;
+ }
+
+ datap = pkh->mpi;
+ endp = datap + ukp->datalen;
+
+ for (i = 0; i < pkh->nmpi; i++) {
+ unsigned int remaining = endp - datap;
+ pkey[i] = mpi_read_from_buffer(datap, &remaining);
+ datap += remaining;
+ }
+
+ mblen = mpi_get_nbits(pkey[0]);
+ mlen = (mblen + 7)/8;
+
+ out1 = kzalloc(mlen, GFP_KERNEL);
+ if (!out1)
+ goto err;
+
+ out2 = 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);
+
+ err = -EINVAL;
+ pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len, &valid);
+
+ if (valid && len == hlen)
+ err = memcmp(out2, h, hlen);
+
+err:
+ mpi_free(in);
+ mpi_free(res);
+ kfree(out1);
+ kfree(out2);
+ mpi_free(pkey[0]);
+ mpi_free(pkey[1]);
+err1:
+ up_read(&key->sem);
+
+ return err;
+}
+
+/*
+ * Signature verification with public key
+ */
+int ksign_verify(const char *sig, int siglen,
+ const char *digest, int digestlen)
+{
+ int err = -ENOMEM;
+ struct signature_hdr *sh = (struct signature_hdr *)sig;
+ struct shash_desc *desc = NULL;
+ unsigned char h[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));
+
+ key = request_key(&key_type_user, name, NULL);
+ if (IS_ERR(key)) {
+ pr_err("key not found, id: %s\n", name);
+ return -ENOENT;
+ }
+
+ 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, digest, digestlen);
+ crypto_shash_update(desc, sig, sizeof(*sh));
+ crypto_shash_final(desc, h);
+
+ kfree(desc);
+
+ /* pass signature mpis address */
+ err = ksign_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
+ h, sizeof(h));
+
+err:
+ key_put(key);
+
+ if (err)
+ pr_info("ksign_verify: %d\n", err);
+
+ return err ? -EINVAL : 0;
+}
+EXPORT_SYMBOL_GPL(ksign_verify);
+
+static int __init ksign_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 ksign_cleanup(void)
+{
+ crypto_free_shash(shash);
+}
+
+module_init(ksign_init);
+module_exit(ksign_cleanup);
+
+MODULE_LICENSE("GPL");
diff --git a/include/linux/crypto/ksign.h b/include/linux/crypto/ksign.h
new file mode 100644
index 0000000..f1e47cb
--- /dev/null
+++ b/include/linux/crypto/ksign.h
@@ -0,0 +1,48 @@
+#ifndef CRYPTO_KSIGN_H
+#define CRYPTO_KSIGN_H
+
+enum pubkey_type {
+ PUBKEY_ALGO_RSA,
+ PUBKEY_ALGO_DSA,
+ PUBKEY_ALGO_MAX,
+};
+
+enum digest_algo {
+ DIGEST_ALGO_SHA1,
+ DIGEST_ALGO_SHA256,
+ DIGEST_ALGO_MAX
+};
+
+struct pubkey_hdr {
+ uint8_t version;
+ uint8_t algo;
+ uint8_t nmpi;
+ char mpi[0];
+} __attribute__ ((packed));
+
+struct signature_hdr {
+ uint8_t version;
+ time_t timestamp; /* signature made */
+ uint8_t algo;
+ uint8_t hash;
+ uint8_t keyid[8];
+ uint8_t nmpi;
+ char mpi[0];
+} __attribute__ ((packed));
+
+#ifdef CONFIG_CRYPTO_KSIGN
+
+int ksign_verify(const char *sig, int siglen,
+ const char *digest, int digestlen);
+
+#else
+
+static inline int ksign_verify(const char *sig, int siglen,
+ const char *digest, int digestlen)
+{
+ return -EOPNOTSUPP;
+}
+
+#endif /* CONFIG_CRYPTO_KSIGN */
+
+#endif /* CRYPTO_KSIGN_H */
--
1.7.4.1


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