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SubjectRe: [PATCH V4 02/15] asymmetric keys: implement EMSA_PKCS1-v1_5-ENCODE in rsa
On Sun, Sep 15, 2013 at 08:56:48AM +0800, Lee, Chun-Yi wrote:
> Implement EMSA_PKCS1-v1_5-ENCODE [RFC3447 sec 9.2] in rsa.c. It's the
> first step of signature generation operation (RSASSA-PKCS1-v1_5-SIGN).
>
> This patch is temporary set emLen to pks->k, and temporary set EM to
> pks->S for debugging. We will replace the above values to real signature
> after implement RSASP1.
>
> The naming of EMSA_PKCS1_v1_5_ENCODE and the variables used in this function
> accord PKCS#1 spec but not follow kernel naming convention, it useful when look
> at them with spec.
>
> Reference: ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1v2/pkcs1ietffinal.txt
> Reference: http://www.emc.com/collateral/white-papers/h11300-pkcs-1v2-2-rsa-cryptography-standard-wp.pdf
>
> V2:

You're now at V4.

> - Clean up naming of variable: replace _EM by EM, replace EM by EM_tmp.
> - Add comment to EMSA_PKCS1-v1_5-ENCODE function.
>
> Cc: Pavel Machek <pavel@ucw.cz>
> Reviewed-by: Jiri Kosina <jkosina@suse.cz>
> Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
> ---
> crypto/asymmetric_keys/rsa.c | 163 +++++++++++++++++++++++++++++++++++++++++-
> include/crypto/public_key.h | 2 +
> 2 files changed, 164 insertions(+), 1 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/rsa.c b/crypto/asymmetric_keys/rsa.c
> index 47f3be4..352ba45 100644
> --- a/crypto/asymmetric_keys/rsa.c
> +++ b/crypto/asymmetric_keys/rsa.c
> @@ -13,6 +13,7 @@
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/slab.h>
> +#include <crypto/hash.h>
> #include "public_key.h"
> #include "private_key.h"
>
> @@ -152,6 +153,132 @@ static int RSA_I2OSP(MPI x, size_t xLen, u8 **_X)
> }
>
> /*
> + * EMSA_PKCS1-v1_5-ENCODE [RFC3447 sec 9.2]
> + * @M: message to be signed, an octet string
> + * @emLen: intended length in octets of the encoded message
> + * @hash_algo: hash function (option)
> + * @hash: true means hash M, otherwise M is already a digest
> + * @EM: encoded message, an octet string of length emLen
> + *
> + * This function is a implementation of the EMSA-PKCS1-v1_5 encoding operation
> + * in RSA PKCS#1 spec. It used by the signautre generation operation of
> + * RSASSA-PKCS1-v1_5 to encode message M to encoded message EM.
> + *
> + * The variables used in this function accord PKCS#1 spec but not follow kernel
> + * naming convention, it useful when look at them with spec.
> + */
> +static int EMSA_PKCS1_v1_5_ENCODE(const u8 *M, size_t emLen,
> + enum pkey_hash_algo hash_algo, const bool hash,
> + u8 **EM, struct public_key_signature *pks)
> +{
> + u8 *digest;
> + struct crypto_shash *tfm;
> + struct shash_desc *desc;
> + size_t digest_size, desc_size;
> + size_t tLen;
> + u8 *T, *PS, *EM_tmp;
> + int i, ret;
> +
> + pr_info("EMSA_PKCS1_v1_5_ENCODE start\n");
> +
> + if (!RSA_ASN1_templates[hash_algo].data)
> + ret = -ENOTSUPP;

...

> + else
> + pks->pkey_hash_algo = hash_algo;
> +
> + /* 1) Apply the hash function to the message M to produce a hash value H */
> + tfm = crypto_alloc_shash(pkey_hash_algo[hash_algo], 0, 0);
> + if (IS_ERR(tfm))
> + return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
> +
> + desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
> + digest_size = crypto_shash_digestsize(tfm);
> +
> + ret = -ENOMEM;

The earlier "ret = -ENOTSUPP;" is either unused because you return at the IS_ERR,
or unused because you overwrite it here. I'm a little disappointed that
the compiler didn't recognise that something was assigned to a value that
is never used.

Phil

> +
> + digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
> + if (!digest)
> + goto error_digest;
> + pks->digest = digest;
> + pks->digest_size = digest_size;
> +
> + if (hash) {
> + desc = (void *) digest + digest_size;
> + desc->tfm = tfm;
> + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
> +
> + ret = crypto_shash_init(desc);
> + if (ret < 0)
> + goto error_shash;
> + ret = crypto_shash_finup(desc, M, sizeof(M), pks->digest);
> + if (ret < 0)
> + goto error_shash;
> + } else {
> + memcpy(pks->digest, M, pks->digest_size);
> + pks->digest_size = digest_size;
> + }
> + crypto_free_shash(tfm);
> +
> + /* 2) Encode the algorithm ID for the hash function and the hash value into
> + * an ASN.1 value of type DigestInfo with the DER. Let T be the DER encoding of
> + * the DigestInfo value and let tLen be the length in octets of T.
> + */
> + tLen = RSA_ASN1_templates[hash_algo].size + pks->digest_size;
> + T = kmalloc(tLen, GFP_KERNEL);
> + if (!T)
> + goto error_T;
> +
> + memcpy(T, RSA_ASN1_templates[hash_algo].data, RSA_ASN1_templates[hash_algo].size);
> + memcpy(T + RSA_ASN1_templates[hash_algo].size, pks->digest, pks->digest_size);
> +
> + /* 3) check If emLen < tLen + 11, output "intended encoded message length too short" */
> + if (emLen < tLen + 11) {
> + ret = -EINVAL;
> + goto error_emLen;
> + }
> +
> + /* 4) Generate an octet string PS consisting of emLen - tLen - 3 octets with 0xff. */
> + PS = kmalloc(emLen - tLen - 3, GFP_KERNEL);
> + if (!PS)
> + goto error_P;
> +
> + for (i = 0; i < (emLen - tLen - 3); i++)
> + PS[i] = 0xff;
> +
> + /* 5) Concatenate PS, the DER encoding T, and other padding to form the encoded
> + * message EM as EM = 0x00 || 0x01 || PS || 0x00 || T
> + */
> + EM_tmp = kmalloc(3 + emLen - tLen - 3 + tLen, GFP_KERNEL);
> + if (!EM_tmp)
> + goto error_EM;
> +
> + EM_tmp[0] = 0x00;
> + EM_tmp[1] = 0x01;
> + memcpy(EM_tmp + 2, PS, emLen - tLen - 3);
> + EM_tmp[2 + emLen - tLen - 3] = 0x00;
> + memcpy(EM_tmp + 2 + emLen - tLen - 3 + 1, T, tLen);
> +
> + *EM = EM_tmp;
> +
> + kfree(PS);
> + kfree(T);
> +
> + return 0;
> +
> +error_EM:
> + kfree(PS);
> +error_P:
> +error_emLen:
> + kfree(T);
> +error_T:
> +error_shash:
> + kfree(digest);
> +error_digest:
> + crypto_free_shash(tfm);
> + return ret;
> +}
> +
> +/*
> * Perform the RSA signature verification.
> * @H: Value of hash of data and metadata
> * @EM: The computed signature value
> @@ -275,9 +402,43 @@ static struct public_key_signature *RSA_generate_signature(
> const struct private_key *key, u8 *M,
> enum pkey_hash_algo hash_algo, const bool hash)
> {
> + struct public_key_signature *pks;
> + u8 *EM = NULL;
> + size_t emLen;
> + int ret;
> +
> pr_info("RSA_generate_signature start\n");
>
> - return 0;
> + ret = -ENOMEM;
> + pks = kzalloc(sizeof(*pks), GFP_KERNEL);
> + if (!pks)
> + goto error_no_pks;
> +
> + /* 1): EMSA-PKCS1-v1_5 encoding: */
> + /* Use the private key modulus size to be EM length */
> + emLen = mpi_get_nbits(key->rsa.n);
> + emLen = (emLen + 7) / 8;
> +
> + ret = EMSA_PKCS1_v1_5_ENCODE(M, emLen, hash_algo, hash, &EM, pks);
> + if (ret < 0)
> + goto error_v1_5_encode;
> +
> + /* TODO 2): m = OS2IP (EM) */
> +
> + /* TODO 3): s = RSASP1 (K, m) */
> +
> + /* TODO 4): S = I2OSP (s, k) */
> +
> + /* TODO: signature S to a u8* S or set to sig->rsa.s? */
> + pks->S = EM; /* TODO: temporary set S to EM */
> +
> + return pks;
> +
> +error_v1_5_encode:
> + kfree(pks);
> +error_no_pks:
> + pr_info("<==%s() = %d\n", __func__, ret);
> + return ERR_PTR(ret);
> }
>
> const struct public_key_algorithm RSA_public_key_algorithm = {
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index d44b29f..1cdf457 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -110,6 +110,8 @@ extern void public_key_destroy(void *payload);
> struct public_key_signature {
> u8 *digest;
> u8 digest_size; /* Number of bytes in digest */
> + u8 *S; /* signature S of length k octets */
> + size_t k; /* length k of signature S */
> u8 nr_mpi; /* Occupancy of mpi[] */
> enum pkey_hash_algo pkey_hash_algo : 8;
> union {
> --
> 1.6.0.2
>
> --
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