rsa.c

Go to the documentation of this file.

/*
 * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <stdint.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
#include <ipxe/asn1.h>
#include <ipxe/crypto.h>
#include <ipxe/bigint.h>
#include <ipxe/random_nz.h>
#include <ipxe/rsa.h>

/** @file
 *
 * RSA public-key cryptography
 *
 * RSA is documented in RFC 3447.
 */

/* Disambiguate the various error causes */
#define EACCES_VERIFY \
        __einfo_error ( EINFO_EACCES_VERIFY )
#define EINFO_EACCES_VERIFY \
        __einfo_uniqify ( EINFO_EACCES, 0x01, "RSA signature incorrect" )

/**
 * Identify RSA prefix
 *
 * @v digest            Digest algorithm
 * @ret prefix          RSA prefix, or NULL
 */
static struct rsa_digestinfo_prefix *
rsa_find_prefix ( struct digest_algorithm *digest ) {
        struct rsa_digestinfo_prefix *prefix;

        for_each_table_entry ( prefix, RSA_DIGESTINFO_PREFIXES ) {
                if ( prefix->digest == digest )
                        return prefix;
        }
        return NULL;
}

/**
 * Free RSA dynamic storage
 *
 * @v context           RSA context
 */
static void rsa_free ( struct rsa_context *context ) {

        free ( context->dynamic );
        context->dynamic = NULL;
}

/**
 * Allocate RSA dynamic storage
 *
 * @v context           RSA context
 * @v modulus_len       Modulus length
 * @v exponent_len      Exponent length
 * @ret rc              Return status code
 */
static int rsa_alloc ( struct rsa_context *context, size_t modulus_len,
                       size_t exponent_len ) {
        unsigned int size = bigint_required_size ( modulus_len );
        unsigned int exponent_size = bigint_required_size ( exponent_len );
        bigint_t ( size ) *modulus;
        bigint_t ( exponent_size ) *exponent;
        size_t tmp_len = bigint_mod_exp_tmp_len ( modulus, exponent );
        struct {
                bigint_t ( size ) modulus;
                bigint_t ( exponent_size ) exponent;
                bigint_t ( size ) input;
                bigint_t ( size ) output;
                uint8_t tmp[tmp_len];
        } __attribute__ (( packed )) *dynamic;

        /* Free any existing dynamic storage */
        rsa_free ( context );

        /* Allocate dynamic storage */
        dynamic = malloc ( sizeof ( *dynamic ) );
        if ( ! dynamic )
                return -ENOMEM;

        /* Assign dynamic storage */
        context->dynamic = dynamic;
        context->modulus0 = &dynamic->modulus.element[0];
        context->size = size;
        context->max_len = modulus_len;
        context->exponent0 = &dynamic->exponent.element[0];
        context->exponent_size = exponent_size;
        context->input0 = &dynamic->input.element[0];
        context->output0 = &dynamic->output.element[0];
        context->tmp = &dynamic->tmp;

        return 0;
}

/**
 * Parse RSA integer
 *
 * @v integer           Integer to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int rsa_parse_integer ( struct asn1_cursor *integer,
                               const struct asn1_cursor *raw ) {

        /* Enter integer */
        memcpy ( integer, raw, sizeof ( *integer ) );
        asn1_enter ( integer, ASN1_INTEGER );

        /* Skip initial sign byte if applicable */
        if ( ( integer->len > 1 ) &&
             ( *( ( uint8_t * ) integer->data ) == 0x00 ) ) {
                integer->data++;
                integer->len--;
        }

        /* Fail if cursor or integer are invalid */
        if ( ! integer->len )
                return -EINVAL;

        return 0;
}

/**
 * Parse RSA modulus and exponent
 *
 * @v modulus           Modulus to fill in
 * @v exponent          Exponent to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int rsa_parse_mod_exp ( struct asn1_cursor *modulus,
                               struct asn1_cursor *exponent,
                               const struct asn1_cursor *raw ) {
        struct asn1_bit_string bits;
        struct asn1_cursor cursor;
        int is_private;
        int rc;

        /* Enter subjectPublicKeyInfo/RSAPrivateKey */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Determine key format */
        if ( asn1_type ( &cursor ) == ASN1_INTEGER ) {

                /* Private key */
                is_private = 1;

                /* Skip version */
                asn1_skip_any ( &cursor );

        } else {

                /* Public key */
                is_private = 0;

                /* Skip algorithm */
                asn1_skip ( &cursor, ASN1_SEQUENCE );

                /* Enter subjectPublicKey */
                if ( ( rc = asn1_integral_bit_string ( &cursor, &bits ) ) != 0 )
                        return rc;
                cursor.data = bits.data;
                cursor.len = bits.len;

                /* Enter RSAPublicKey */
                asn1_enter ( &cursor, ASN1_SEQUENCE );
        }

        /* Extract modulus */
        if ( ( rc = rsa_parse_integer ( modulus, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Skip public exponent, if applicable */
        if ( is_private )
                asn1_skip ( &cursor, ASN1_INTEGER );

        /* Extract publicExponent/privateExponent */
        if ( ( rc = rsa_parse_integer ( exponent, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Initialise RSA cipher
 *
 * @v ctx               RSA context
 * @v key               Key
 * @v key_len           Length of key
 * @ret rc              Return status code
 */
static int rsa_init ( void *ctx, const void *key, size_t key_len ) {
        struct rsa_context *context = ctx;
        struct asn1_cursor modulus;
        struct asn1_cursor exponent;
        struct asn1_cursor cursor;
        int rc;

        /* Initialise context */
        memset ( context, 0, sizeof ( *context ) );

        /* Initialise cursor */
        cursor.data = key;
        cursor.len = key_len;

        /* Parse modulus and exponent */
        if ( ( rc = rsa_parse_mod_exp ( &modulus, &exponent, &cursor ) ) != 0 ){
                DBGC ( context, "RSA %p invalid modulus/exponent:\n", context );
                DBGC_HDA ( context, 0, cursor.data, cursor.len );
                goto err_parse;
        }

        DBGC ( context, "RSA %p modulus:\n", context );
        DBGC_HDA ( context, 0, modulus.data, modulus.len );
        DBGC ( context, "RSA %p exponent:\n", context );
        DBGC_HDA ( context, 0, exponent.data, exponent.len );

        /* Allocate dynamic storage */
        if ( ( rc = rsa_alloc ( context, modulus.len, exponent.len ) ) != 0 )
                goto err_alloc;

        /* Construct big integers */
        bigint_init ( ( ( bigint_t ( context->size ) * ) context->modulus0 ),
                      modulus.data, modulus.len );
        bigint_init ( ( ( bigint_t ( context->exponent_size ) * )
                        context->exponent0 ), exponent.data, exponent.len );

        return 0;

        rsa_free ( context );
 err_alloc:
 err_parse:
        return rc;
}

/**
 * Calculate RSA maximum output length
 *
 * @v ctx               RSA context
 * @ret max_len         Maximum output length
 */
static size_t rsa_max_len ( void *ctx ) {
        struct rsa_context *context = ctx;

        return context->max_len;
}

/**
 * Perform RSA cipher operation
 *
 * @v context           RSA context
 * @v in                Input buffer
 * @v out               Output buffer
 */
static void rsa_cipher ( struct rsa_context *context,
                         const void *in, void *out ) {
        bigint_t ( context->size ) *input = ( ( void * ) context->input0 );
        bigint_t ( context->size ) *output = ( ( void * ) context->output0 );
        bigint_t ( context->size ) *modulus = ( ( void * ) context->modulus0 );
        bigint_t ( context->exponent_size ) *exponent =
                ( ( void * ) context->exponent0 );

        /* Initialise big integer */
        bigint_init ( input, in, context->max_len );

        /* Perform modular exponentiation */
        bigint_mod_exp ( input, modulus, exponent, output, context->tmp );

        /* Copy out result */
        bigint_done ( output, out, context->max_len );
}

/**
 * Encrypt using RSA
 *
 * @v ctx               RSA context
 * @v plaintext         Plaintext
 * @v plaintext_len     Length of plaintext
 * @v ciphertext        Ciphertext
 * @ret ciphertext_len  Length of ciphertext, or negative error
 */
static int rsa_encrypt ( void *ctx, const void *plaintext,
                         size_t plaintext_len, void *ciphertext ) {
        struct rsa_context *context = ctx;
        void *temp;
        uint8_t *encoded;
        size_t max_len = ( context->max_len - 11 );
        size_t random_nz_len = ( max_len - plaintext_len + 8 );
        int rc;

        /* Sanity check */
        if ( plaintext_len > max_len ) {
                DBGC ( context, "RSA %p plaintext too long (%zd bytes, max "
                       "%zd)\n", context, plaintext_len, max_len );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p encrypting:\n", context );
        DBGC_HDA ( context, 0, plaintext, plaintext_len );

        /* Construct encoded message (using the big integer output
         * buffer as temporary storage)
         */
        temp = context->output0;
        encoded = temp;
        encoded[0] = 0x00;
        encoded[1] = 0x02;
        if ( ( rc = get_random_nz ( &encoded[2], random_nz_len ) ) != 0 ) {
                DBGC ( context, "RSA %p could not generate random data: %s\n",
                       context, strerror ( rc ) );
                return rc;
        }
        encoded[ 2 + random_nz_len ] = 0x00;
        memcpy ( &encoded[ context->max_len - plaintext_len ],
                 plaintext, plaintext_len );

        /* Encipher the encoded message */
        rsa_cipher ( context, encoded, ciphertext );
        DBGC ( context, "RSA %p encrypted:\n", context );
        DBGC_HDA ( context, 0, ciphertext, context->max_len );

        return context->max_len;
}

/**
 * Decrypt using RSA
 *
 * @v ctx               RSA context
 * @v ciphertext        Ciphertext
 * @v ciphertext_len    Ciphertext length
 * @v plaintext         Plaintext
 * @ret plaintext_len   Plaintext length, or negative error
 */
static int rsa_decrypt ( void *ctx, const void *ciphertext,
                         size_t ciphertext_len, void *plaintext ) {
        struct rsa_context *context = ctx;
        void *temp;
        uint8_t *encoded;
        uint8_t *end;
        uint8_t *zero;
        uint8_t *start;
        size_t plaintext_len;

        /* Sanity check */
        if ( ciphertext_len != context->max_len ) {
                DBGC ( context, "RSA %p ciphertext incorrect length (%zd "
                       "bytes, should be %zd)\n",
                       context, ciphertext_len, context->max_len );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p decrypting:\n", context );
        DBGC_HDA ( context, 0, ciphertext, ciphertext_len );

        /* Decipher the message (using the big integer input buffer as
         * temporary storage)
         */
        temp = context->input0;
        encoded = temp;
        rsa_cipher ( context, ciphertext, encoded );

        /* Parse the message */
        end = ( encoded + context->max_len );
        if ( ( encoded[0] != 0x00 ) || ( encoded[1] != 0x02 ) )
                goto invalid;
        zero = memchr ( &encoded[2], 0, ( end - &encoded[2] ) );
        if ( ! zero )
                goto invalid;
        start = ( zero + 1 );
        plaintext_len = ( end - start );

        /* Copy out message */
        memcpy ( plaintext, start, plaintext_len );
        DBGC ( context, "RSA %p decrypted:\n", context );
        DBGC_HDA ( context, 0, plaintext, plaintext_len );

        return plaintext_len;

 invalid:
        DBGC ( context, "RSA %p invalid decrypted message:\n", context );
        DBGC_HDA ( context, 0, encoded, context->max_len );
        return -EINVAL;
}

/**
 * Encode RSA digest
 *
 * @v context           RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v encoded           Encoded digest
 * @ret rc              Return status code
 */
static int rsa_encode_digest ( struct rsa_context *context,
                               struct digest_algorithm *digest,
                               const void *value, void *encoded ) {
        struct rsa_digestinfo_prefix *prefix;
        size_t digest_len = digest->digestsize;
        uint8_t *temp = encoded;
        size_t digestinfo_len;
        size_t max_len;
        size_t pad_len;

        /* Identify prefix */
        prefix = rsa_find_prefix ( digest );
        if ( ! prefix ) {
                DBGC ( context, "RSA %p has no prefix for %s\n",
                       context, digest->name );
                return -ENOTSUP;
        }
        digestinfo_len = ( prefix->len + digest_len );

        /* Sanity check */
        max_len = ( context->max_len - 11 );
        if ( digestinfo_len > max_len ) {
                DBGC ( context, "RSA %p %s digestInfo too long (%zd bytes, max"
                       "%zd)\n",
                       context, digest->name, digestinfo_len, max_len );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p encoding %s digest:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, value, digest_len );

        /* Construct encoded message */
        *(temp++) = 0x00;
        *(temp++) = 0x01;
        pad_len = ( max_len - digestinfo_len + 8 );
        memset ( temp, 0xff, pad_len );
        temp += pad_len;
        *(temp++) = 0x00;
        memcpy ( temp, prefix->data, prefix->len );
        temp += prefix->len;
        memcpy ( temp, value, digest_len );
        temp += digest_len;
        assert ( temp == ( encoded + context->max_len ) );
        DBGC ( context, "RSA %p encoded %s digest:\n", context, digest->name );
        DBGC_HDA ( context, 0, encoded, context->max_len );

        return 0;
}

/**
 * Sign digest value using RSA
 *
 * @v ctx               RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v signature         Signature
 * @ret signature_len   Signature length, or negative error
 */
static int rsa_sign ( void *ctx, struct digest_algorithm *digest,
                      const void *value, void *signature ) {
        struct rsa_context *context = ctx;
        void *temp;
        int rc;

        DBGC ( context, "RSA %p signing %s digest:\n", context, digest->name );
        DBGC_HDA ( context, 0, value, digest->digestsize );

        /* Encode digest (using the big integer output buffer as
         * temporary storage)
         */
        temp = context->output0;
        if ( ( rc = rsa_encode_digest ( context, digest, value, temp ) ) != 0 )
                return rc;

        /* Encipher the encoded digest */
        rsa_cipher ( context, temp, signature );
        DBGC ( context, "RSA %p signed %s digest:\n", context, digest->name );
        DBGC_HDA ( context, 0, signature, context->max_len );

        return context->max_len;
}

/**
 * Verify signed digest value using RSA
 *
 * @v ctx               RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v signature         Signature
 * @v signature_len     Signature length
 * @ret rc              Return status code
 */
static int rsa_verify ( void *ctx, struct digest_algorithm *digest,
                        const void *value, const void *signature,
                        size_t signature_len ) {
        struct rsa_context *context = ctx;
        void *temp;
        void *expected;
        void *actual;
        int rc;

        /* Sanity check */
        if ( signature_len != context->max_len ) {
                DBGC ( context, "RSA %p signature incorrect length (%zd "
                       "bytes, should be %zd)\n",
                       context, signature_len, context->max_len );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p verifying %s digest:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, value, digest->digestsize );
        DBGC_HDA ( context, 0, signature, signature_len );

        /* Decipher the signature (using the big integer input buffer
         * as temporary storage)
         */
        temp = context->input0;
        expected = temp;
        rsa_cipher ( context, signature, expected );
        DBGC ( context, "RSA %p deciphered signature:\n", context );
        DBGC_HDA ( context, 0, expected, context->max_len );

        /* Encode digest (using the big integer output buffer as
         * temporary storage)
         */
        temp = context->output0;
        actual = temp;
        if ( ( rc = rsa_encode_digest ( context, digest, value, actual ) ) !=0 )
                return rc;

        /* Verify the signature */
        if ( memcmp ( actual, expected, context->max_len ) != 0 ) {
                DBGC ( context, "RSA %p signature verification failed\n",
                       context );
                return -EACCES_VERIFY;
        }

        DBGC ( context, "RSA %p signature verified successfully\n", context );
        return 0;
}

/**
 * Finalise RSA cipher
 *
 * @v ctx               RSA context
 */
static void rsa_final ( void *ctx ) {
        struct rsa_context *context = ctx;

        rsa_free ( context );
}

/**
 * Check for matching RSA public/private key pair
 *
 * @v private_key       Private key
 * @v private_key_len   Private key length
 * @v public_key        Public key
 * @v public_key_len    Public key length
 * @ret rc              Return status code
 */
static int rsa_match ( const void *private_key, size_t private_key_len,
                       const void *public_key, size_t public_key_len ) {
        struct asn1_cursor private_modulus;
        struct asn1_cursor private_exponent;
        struct asn1_cursor private_cursor;
        struct asn1_cursor public_modulus;
        struct asn1_cursor public_exponent;
        struct asn1_cursor public_cursor;
        int rc;

        /* Initialise cursors */
        private_cursor.data = private_key;
        private_cursor.len = private_key_len;
        public_cursor.data = public_key;
        public_cursor.len = public_key_len;

        /* Parse moduli and exponents */
        if ( ( rc = rsa_parse_mod_exp ( &private_modulus, &private_exponent,
                                        &private_cursor ) ) != 0 )
                return rc;
        if ( ( rc = rsa_parse_mod_exp ( &public_modulus, &public_exponent,
                                        &public_cursor ) ) != 0 )
                return rc;

        /* Compare moduli */
        if ( asn1_compare ( &private_modulus, &public_modulus ) != 0 )
                return -ENOTTY;

        return 0;
}

/** RSA public-key algorithm */
struct pubkey_algorithm rsa_algorithm = {
        .name           = "rsa",
        .ctxsize        = RSA_CTX_SIZE,
        .init           = rsa_init,
        .max_len        = rsa_max_len,
        .encrypt        = rsa_encrypt,
        .decrypt        = rsa_decrypt,
        .sign           = rsa_sign,
        .verify         = rsa_verify,
        .final          = rsa_final,
        .match          = rsa_match,
};

/* Drag in objects via rsa_algorithm */
REQUIRING_SYMBOL ( rsa_algorithm );

/* Drag in crypto configuration */
REQUIRE_OBJECT ( config_crypto );