From: David Howells Subject: [PATCH 10/21] KEYS: DSA signature verification algorithm [ver #3] Date: Fri, 02 Dec 2011 18:44:31 +0000 Message-ID: <20111202184431.21874.52240.stgit@warthog.procyon.org.uk> References: <20111202184229.21874.25782.stgit@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: linux-crypto@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dmitry.kasatkin@intel.com, zohar@linux.vnet.ibm.com, arjan.van.de.ven@intel.com, alan.cox@intel.com, David Howells To: keyrings@linux-nfs.org Return-path: In-Reply-To: <20111202184229.21874.25782.stgit@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org Implement the DSA algorithm (FIPS-186). At this time, only signature verification is supported. This uses the asymmetric public key subtype to hold its key data. Signed-off-by: David Howells --- security/keys/Kconfig | 7 ++ security/keys/Makefile | 1 security/keys/crypto_dsa.c | 126 ++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 134 insertions(+), 0 deletions(-) create mode 100644 security/keys/crypto_dsa.c diff --git a/security/keys/Kconfig b/security/keys/Kconfig index 07c7f3b..76de2ba 100644 --- a/security/keys/Kconfig +++ b/security/keys/Kconfig @@ -86,3 +86,10 @@ config CRYPTO_KEY_PUBLIC_KEY_SUBTYPE If signature generation and/or verification are to be used, appropriate hash algorithms (such as SHA-1) must be available. ENOPKG will be reported if the requisite algorithm is unavailable. + +config CRYPTO_KEY_PKEY_ALGO_DSA + tristate "DSA public-key algorithm" + depends on CRYPTO_KEY_PUBLIC_KEY_SUBTYPE + help + This option enables support for the DSA public key algorithm + (FIPS-186). diff --git a/security/keys/Makefile b/security/keys/Makefile index dc3281f..5f1c627 100644 --- a/security/keys/Makefile +++ b/security/keys/Makefile @@ -26,5 +26,6 @@ obj-$(CONFIG_TRUSTED_KEYS) += trusted.o obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted-keys/ obj-$(CONFIG_CRYPTO_KEY_TYPE) += crypto_keys.o obj-$(CONFIG_CRYPTO_KEY_PUBLIC_KEY_SUBTYPE) += public_key.o +obj-$(CONFIG_CRYPTO_KEY_PKEY_ALGO_DSA) += crypto_dsa.o crypto_keys-y := crypto_type.o crypto_verify.o diff --git a/security/keys/crypto_dsa.c b/security/keys/crypto_dsa.c new file mode 100644 index 0000000..26b86f2 --- /dev/null +++ b/security/keys/crypto_dsa.c @@ -0,0 +1,126 @@ +/* DSA asymmetric public-key algorithm + * + * Copyright (C) 2011 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public Licence + * as published by the Free Software Foundation; either version + * 2 of the Licence, or (at your option) any later version. + */ + +#define pr_fmt(fmt) "DSA: "fmt +#include +#include +#include "public_key.h" + +MODULE_LICENSE("GPL"); + +#define kenter(FMT, ...) \ + pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__) +#define kleave(FMT, ...) \ + pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__) + +/* + * Perform the actual mathematical DSA signature verification. + */ +static int DSA_verify(const MPI datahash, + const struct public_key_signature *sig, + const struct public_key *key) +{ + MPI w = NULL, u1 = NULL, u2 = NULL, v = NULL; + MPI base[3]; + MPI exp[3]; + int rc; + + kenter(""); + + if (!(mpi_cmp_ui(sig->dsa.r, 0) > 0 && + mpi_cmp(sig->dsa.r, key->dsa.q) < 0)) { + pr_warning("Assertion failed [0 < r < q]\n"); + return -EKEYREJECTED; + } + + if (!(mpi_cmp_ui(sig->dsa.s, 0) > 0 && + mpi_cmp(sig->dsa.s, key->dsa.q) < 0)) { + pr_warning("Assertion failed [0 < s < q]\n"); + return -EKEYREJECTED; + } + + rc = -ENOMEM; + w = mpi_alloc(mpi_get_nlimbs(key->dsa.q)); if (!w ) goto cleanup; + u1 = mpi_alloc(mpi_get_nlimbs(key->dsa.q)); if (!u1) goto cleanup; + u2 = mpi_alloc(mpi_get_nlimbs(key->dsa.q)); if (!u2) goto cleanup; + v = mpi_alloc(mpi_get_nlimbs(key->dsa.p)); if (!v ) goto cleanup; + + /* w = s^(-1) mod q */ + if (mpi_invm(w, sig->dsa.s, key->dsa.q) < 0) + goto cleanup; + + /* u1 = (datahash * w) mod q */ + if (mpi_mulm(u1, datahash, w, key->dsa.q) < 0) + goto cleanup; + + /* u2 = r * w mod q */ + if (mpi_mulm(u2, sig->dsa.r, w, key->dsa.q) < 0) + goto cleanup; + + /* v = g^u1 * y^u2 mod p mod q */ + base[0] = key->dsa.g; exp[0] = u1; + base[1] = key->dsa.y; exp[1] = u2; + base[2] = NULL; exp[2] = NULL; + + if (mpi_mulpowm(v, base, exp, key->dsa.p) < 0) + goto cleanup; + + if (mpi_fdiv_r(v, v, key->dsa.q) < 0) + goto cleanup; + + rc = (mpi_cmp(v, sig->dsa.r) == 0) ? 0 : -EKEYREJECTED; + +cleanup: + mpi_free(w); + mpi_free(u1); + mpi_free(u2); + mpi_free(v); + kleave(" = %d", rc); + return rc; +} + +/* + * Perform the verification step. + */ +static int DSA_verify_signature(const struct public_key *key, + const struct public_key_signature *sig) +{ + MPI datahash = NULL; + int ret; + + kenter(""); + + ret = -ENOMEM; + datahash = mpi_alloc((sig->digest_size + BYTES_PER_MPI_LIMB - 1) / + BYTES_PER_MPI_LIMB); + if (!datahash) + goto error; + + ret = mpi_set_buffer(datahash, sig->digest, sig->digest_size, 0); + if (ret < 0) + goto error; + + ret = DSA_verify(datahash, sig, key); + +error: + mpi_free(datahash); + kleave(" = %d", ret); + return ret; +} + +const struct public_key_algorithm DSA_public_key_algorithm = { + .name = "DSA", + .n_pub_mpi = 4, + .n_sec_mpi = 1, + .n_sig_mpi = 2, + .verify = DSA_verify_signature, +}; +EXPORT_SYMBOL_GPL(DSA_public_key_algorithm);