rsa.c

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/*
 * 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 );
FILE_SECBOOT ( PERMITTED );
 
#include <byteswap.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <strings.h>
#include <errno.h>
#include <ipxe/asn1.h>
#include <ipxe/crypto.h>
#include <ipxe/bigint.h>
#include <ipxe/random_nz.h>
#include <ipxe/md5_sha1.h>
#include <ipxe/rsa.h>
 
/** @file
 *
 * RSA public-key cryptography
 *
 * RSA is documented in RFC 3447 and updated in RFC 8017.
 */
 
/* 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" )
 
/** An RSA context */
struct rsa_context {
        /** Allocated memory */
        void *dynamic;
        /** Modulus */
        bigint_element_t *modulus0;
        /** Modulus size */
        unsigned int size;
        /** Modulus length */
        size_t max_len;
        /** Exponent */
        bigint_element_t *exponent0;
        /** Exponent size */
        unsigned int exponent_size;
        /** Input buffer */
        bigint_element_t *input0;
        /** Output buffer */
        bigint_element_t *output0;
        /** Temporary working space for modular exponentiation */
        void *tmp;
        /** Modulus MSB mask */
        uint8_t mask;
};
 
/**
 * Encode digest
 *
 * @v context           RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v reference         Reference encoded digest (or NULL)
 * @v encoded           Encoded digest
 * @ret rc              Return status code
 */
typedef int ( rsa_encode_t ) ( struct rsa_context *context,
                               struct digest_algorithm *digest,
                               const void *value, const void *reference,
                               void *encoded );
 
/** Generate random data */
int ( * rsa_get_random ) ( void *data, size_t len ) = get_random_nz;
 
/**
 * 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 inline void rsa_free ( struct rsa_context *context ) {
 
        zfree ( context->dynamic );
}
 
/**
 * 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;
        size_t tmp_len = bigint_mod_exp_tmp_len ( modulus );
        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;
 
        /* 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 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_cursor cursor;
        int is_private;
        int rc;
 
        /* Enter subjectPublicKeyInfo/privateKeyInfo/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 );
 
                /* Enter privateKey, if present */
                if ( asn1_check_algorithm ( &cursor, &rsa_encryption_algorithm,
                                            NULL ) == 0 ) {
 
                        /* Skip privateKeyAlgorithm */
                        asn1_skip_any ( &cursor );
 
                        /* Enter privateKey */
                        asn1_enter ( &cursor, ASN1_OCTET_STRING );
 
                        /* Enter RSAPrivateKey */
                        asn1_enter ( &cursor, ASN1_SEQUENCE );
 
                        /* Skip version */
                        asn1_skip ( &cursor, ASN1_INTEGER );
                }
 
        } else {
 
                /* Public key */
                is_private = 0;
 
                /* Skip algorithm */
                asn1_skip ( &cursor, ASN1_SEQUENCE );
 
                /* Enter subjectPublicKey */
                asn1_enter_bits ( &cursor, NULL );
 
                /* Enter RSAPublicKey */
                asn1_enter ( &cursor, ASN1_SEQUENCE );
        }
 
        /* Extract modulus */
        memcpy ( modulus, &cursor, sizeof ( *modulus ) );
        if ( ( rc = asn1_enter_unsigned ( modulus ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );
 
        /* Skip public exponent, if applicable */
        if ( is_private )
                asn1_skip ( &cursor, ASN1_INTEGER );
 
        /* Extract publicExponent/privateExponent */
        memcpy ( exponent, &cursor, sizeof ( *exponent ) );
        if ( ( rc = asn1_enter_unsigned ( exponent ) ) != 0 )
                return rc;
 
        return 0;
}
 
/**
 * Initialise RSA cipher
 *
 * @v context           RSA context
 * @v key               Key
 * @ret rc              Return status code
 */
static int rsa_init ( struct rsa_context *context,
                      const struct asn1_cursor *key ) {
        struct asn1_cursor modulus;
        struct asn1_cursor exponent;
        uint8_t msb;
        int rc;
 
        /* Initialise context */
        memset ( context, 0, sizeof ( *context ) );
 
        /* Parse modulus and exponent */
        if ( ( rc = rsa_parse_mod_exp ( &modulus, &exponent, key ) ) != 0 ){
                DBGC ( context, "RSA %p invalid modulus/exponent:\n", context );
                DBGC_HDA ( context, 0, key->data, key->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 );
 
        /* Construct MSB mask */
        msb = *( ( const uint8_t * ) modulus.data );
        if ( ! msb ) {
                DBGC ( context, "RSA %p invalid modulus MSB\n", context );
                rc = -EINVAL;
                goto err_msb;
        }
        context->mask = ( ( 1 << ( fls ( msb ) - 1 ) ) - 1 );
 
        /* 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_msb:
 err_parse:
        return rc;
}
 
/**
 * Perform RSA cipher operation
 *
 * @v context           RSA context
 * @v in                Input buffer
 * @v out               Output buffer
 * @ret canonical       Input was in canonical form
 */
static int 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 );
        int canonical;
 
        /* Initialise big integer */
        bigint_init ( input, in, context->max_len );
        canonical = ( ! bigint_is_geq ( input, modulus ) );
 
        /* Perform modular exponentiation */
        bigint_mod_exp ( input, modulus, exponent, output, context->tmp );
 
        /* Copy out result */
        bigint_done ( output, out, context->max_len );
 
        /* Check for canonical input */
        return canonical;
}
 
/**
 * Encrypt using RSA PKCS#1
 *
 * @v pubkey            Public-key algorithm
 * @v key               Key
 * @v plaintext         Plaintext
 * @v ciphertext        Ciphertext
 * @ret ciphertext_len  Length of ciphertext, or negative error
 */
static int rsa_pkcs1_encrypt ( struct pubkey_algorithm *pubkey __unused,
                               const struct asn1_cursor *key,
                               const struct asn1_cursor *plaintext,
                               struct asn1_builder *ciphertext ) {
        struct rsa_context context;
        void *temp;
        uint8_t *encoded;
        size_t min_len;
        size_t pad_len;
        int canonical;
        int rc;
 
        DBGC ( &context, "RSA %p encrypting:\n", &context );
        DBGC_HDA ( &context, 0, plaintext->data, plaintext->len );
 
        /* Initialise context */
        if ( ( rc = rsa_init ( &context, key ) ) != 0 )
                goto err_init;
 
        /* Calculate lengths */
        min_len = ( 1 /* "0x00" */ + 1 /* "0x02" */ + 8 /* minimum padding */
                    + 1 /* "0x00" */ + plaintext->len );
        if ( min_len > context.max_len ) {
                DBGC ( &context, "RSA %p modulus too small for %zd-byte "
                       "plaintext\n", &context, plaintext->len );
                goto err_sanity;
        }
        pad_len = ( 8 /* minimum padding */ + context.max_len - min_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 = rsa_get_random ( &encoded[2], pad_len ) ) != 0 ) {
                DBGC ( &context, "RSA %p could not generate random data: %s\n",
                       &context, strerror ( rc ) );
                goto err_random;
        }
        encoded[ 2 + pad_len ] = 0x00;
        memcpy ( &encoded[ context.max_len - plaintext->len ],
                 plaintext->data, plaintext->len );
        DBGC ( &context, "RSA %p encoded:\n", &context );
        DBGC_HDA ( &context, 0, encoded, context.max_len );
 
        /* Create space for ciphertext */
        if ( ( rc = asn1_grow ( ciphertext, context.max_len ) ) != 0 )
                goto err_grow;
 
        /* Encipher the encoded message */
        canonical = rsa_cipher ( &context, encoded, ciphertext->data );
        assert ( canonical );
        DBGC ( &context, "RSA %p encrypted:\n", &context );
        DBGC_HDA ( &context, 0, ciphertext->data, context.max_len );
 
        /* Free context */
        rsa_free ( &context );
 
        return 0;
 
 err_grow:
 err_random:
 err_sanity:
        rsa_free ( &context );
 err_init:
        return rc;
}
 
/**
 * Decrypt using RSA PKCS#1
 *
 * @v pubkey            Public-key algorithm
 * @v key               Key
 * @v ciphertext        Ciphertext
 * @v plaintext         Plaintext
 * @ret rc              Return status code
 */
static int rsa_pkcs1_decrypt ( struct pubkey_algorithm *pubkey __unused,
                               const struct asn1_cursor *key,
                               const struct asn1_cursor *ciphertext,
                               struct asn1_builder *plaintext ) {
        struct rsa_context context;
        void *temp;
        uint8_t *encoded;
        uint8_t *end;
        uint8_t *pad;
        uint8_t *zero;
        uint8_t *start;
        size_t len;
        int canonical;
        int rc;
 
        DBGC ( &context, "RSA %p decrypting:\n", &context );
        DBGC_HDA ( &context, 0, ciphertext->data, ciphertext->len );
 
        /* Initialise context */
        if ( ( rc = rsa_init ( &context, key ) ) != 0 )
                goto err_init;
 
        /* 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 );
                rc = -ERANGE;
                goto err_sanity;
        }
 
        /* Decipher the message (using the big integer input buffer as
         * temporary storage)
         */
        temp = context.input0;
        encoded = temp;
        canonical = rsa_cipher ( &context, ciphertext->data, encoded );
        DBGC ( &context, "RSA %p encoded:\n", &context );
        DBGC_HDA ( &context, 0, encoded, context.max_len );
        if ( ! canonical ) {
                DBGC ( &context, "RSA %p ciphertext was not canonical\n",
                       &context );
                rc = -EINVAL;
                goto err_canonical;
        }
 
        /* Parse the message */
        end = ( encoded + context.max_len );
        if ( ( encoded[0] != 0x00 ) || ( encoded[1] != 0x02 ) ) {
                rc = -EINVAL;
                goto err_invalid;
        }
        pad = &encoded[2];
        zero = memchr ( pad, 0, ( end - pad ) );
        if ( ( ! zero ) || ( ( zero - pad ) < 8 /* minimum padding */ ) ) {
                DBGC ( &context, "RSA %p invalid decrypted message:\n",
                       &context );
                DBGC_HDA ( &context, 0, encoded, context.max_len );
                rc = -EINVAL;
                goto err_invalid;
        }
        start = ( zero + 1 );
        len = ( end - start );
 
        /* Create space for plaintext */
        if ( ( rc = asn1_grow ( plaintext, len ) ) != 0 )
                goto err_grow;
 
        /* Copy out message */
        memcpy ( plaintext->data, start, len );
        DBGC ( &context, "RSA %p decrypted:\n", &context );
        DBGC_HDA ( &context, 0, plaintext->data, len );
 
        /* Free context */
        rsa_free ( &context );
 
        return 0;
 
 err_grow:
 err_invalid:
 err_canonical:
 err_sanity:
        rsa_free ( &context );
 err_init:
        return rc;
}
 
/**
 * Encode digest using RSA PKCS#1
 *
 * @v context           RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v reference         Reference encoded digest (or NULL)
 * @v encoded           Encoded digest
 * @ret rc              Return status code
 */
static int rsa_pkcs1_encode ( struct rsa_context *context,
                              struct digest_algorithm *digest,
                              const void *value,
                              const void *reference __unused,
                              void *encoded ) {
        struct rsa_digestinfo_prefix *prefix;
        size_t digest_len = digest->digestsize;
        uint8_t *temp = encoded;
        size_t digestinfo_len;
        size_t min_len;
        size_t pad_len;
 
        /* Identify prefix (if any) */
        prefix = rsa_find_prefix ( digest );
        if ( ( ! prefix ) && ( ! is_md5_sha1 ( digest ) ) ) {
                DBGC ( context, "RSA %p has no prefix for %s\n",
                       context, digest->name );
                return -ENOTSUP;
        }
 
        /* Calculate length */
        digestinfo_len = ( digest_len + ( prefix ? prefix->len : 0 ) );
 
        /* Sanity check */
        min_len = ( 1 /* "0x00" */ + 1 /* "0x01" */ + 8 /* minimum padding */
                    + 1 /* "0x00" */ + digestinfo_len );
        if ( min_len > context->max_len ) {
                DBGC ( context, "RSA %p modulus too small for %s digest\n",
                       context, digest->name );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p encoding %s digest using PKCS#1:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, value, digest_len );
 
        /* Construct encoded message */
        *(temp++) = 0x00;
        *(temp++) = 0x01;
        pad_len = ( 8 /* minimum padding */ + context->max_len - min_len );
        memset ( temp, 0xff, pad_len );
        temp += pad_len;
        *(temp++) = 0x00;
        if ( prefix ) {
                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 using PKCS#1:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, encoded, context->max_len );
 
        return 0;
}
 
/**
 * Apply RSA PSS mask generation function
 *
 * @v digest            Digest algorithm
 * @v ctx               Digest context buffer
 * @v out               Digest output buffer
 * @v seed              Mask seed
 * @v xor               XOR buffer
 * @v len               Length of XOR buffer
 */
static void rsa_xor_mask ( struct digest_algorithm *digest, void *ctx,
                           void *out, const void *seed, void *xor,
                           size_t len ) {
        size_t digest_len = digest->digestsize;
        const uint8_t *out_byte = out;
        uint8_t *xor_byte = xor;
        uint32_t counter = 0;
        unsigned int i;
 
        while ( len ) {
 
                /* Generate output */
                digest_init ( digest, ctx );
                digest_update ( digest, ctx, seed, digest_len );
                digest_update ( digest, ctx, &counter, sizeof ( counter ) );
                digest_final ( digest, ctx, out );
 
                /* XOR output into buffer */
                for ( i = 0 ; len && ( i < digest_len ) ; i++, len-- )
                        *(xor_byte++) ^= out_byte[i];
 
                /* Increment counter */
                counter = htonl ( ntohl ( counter ) + 1 );
        }
}
 
/**
 * Encode digest using RSA PSS
 *
 * @v context           RSA context
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v reference         Reference encoded digest (or NULL)
 * @v encoded           Encoded digest
 * @ret rc              Return status code
 */
static int rsa_pss_encode ( struct rsa_context *context,
                            struct digest_algorithm *digest,
                            const void *value, const void *reference,
                            void *encoded ) {
        static uint8_t zero[8];
        uint8_t ctx[ digest->ctxsize ];
        uint8_t out[ digest->digestsize ];
        size_t digest_len = digest->digestsize;
        size_t mask_len;
        size_t pad_len;
        size_t min_len;
        void *hash;
        void *salt;
        uint8_t *msb;
        uint8_t *head;
        uint8_t *tail;
        int rc;
 
        /* Sanity check */
        min_len = ( sizeof ( *head ) + digest_len /* salt */ +
                    digest_len /* hash */ + sizeof ( *tail ) );
        if ( context->max_len < min_len ) {
                DBGC ( context, "RSA %p %s formatted digest value too long "
                       "(%zd bytes, max %zd)\n", context, digest->name,
                       min_len, context->max_len );
                return -ERANGE;
        }
        DBGC ( context, "RSA %p encoding %s digest using PSS:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, value, digest_len );
 
        /* Split message into component parts */
        pad_len = ( context->max_len - min_len );
        msb = encoded;
        head = ( msb + pad_len );
        salt = ( head + sizeof ( *head ) );
        hash = ( salt + digest_len );
        tail = ( hash + digest_len );
        mask_len = ( pad_len + sizeof ( *head ) + digest_len /* salt */ );
        assert ( tail == ( encoded + context->max_len - 1 ) );
 
        /* Generate or construct salt as applicable */
        if ( reference ) {
                memcpy ( encoded, reference, context->max_len );
                rsa_xor_mask ( digest, ctx, out, hash, encoded, mask_len );
        } else {
                if ( ( rc = rsa_get_random ( salt, digest_len ) ) != 0 ) {
                        DBGC ( context, "RSA %p could not generate random "
                               "salt: %s\n", context, strerror ( rc ) );
                        return rc;
                }
        }
        DBGC ( context, "RSA %p salt:\n", context );
        DBGC_HDA ( context, 0, salt, digest_len );
 
        /* Construct intermediate digest */
        digest_init ( digest, ctx );
        digest_update ( digest, ctx, zero, sizeof ( zero ) );
        digest_update ( digest, ctx, value, digest_len );
        digest_update ( digest, ctx, salt, digest_len );
        digest_final ( digest, ctx, hash );
 
        /* Construct message */
        memset ( encoded, 0, pad_len );
        *head = 0x01;
        rsa_xor_mask ( digest, ctx, out, hash, encoded, mask_len );
        *msb &= context->mask;
        *tail = 0xbc;
        DBGC ( context, "RSA %p encoded %s digest using PSS:\n",
               context, digest->name );
        DBGC_HDA ( context, 0, encoded, context->max_len );
 
        return 0;
}
 
/**
 * Sign digest value using RSA
 *
 * @v pubkey            Public-key algorithm
 * @v key               Key
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v signature         Signature
 * @ret rc              Return status code
 */
static int rsa_sign ( struct pubkey_algorithm *pubkey,
                      const struct asn1_cursor *key,
                      struct digest_algorithm *digest, const void *value,
                      struct asn1_builder *signature ) {
        rsa_encode_t *encode = pubkey->priv;
        struct rsa_context context;
        int canonical;
        int rc;
 
        DBGC ( &context, "RSA %p signing %s digest:\n",
               &context, digest->name );
        DBGC_HDA ( &context, 0, value, digest->digestsize );
 
        /* Initialise context */
        if ( ( rc = rsa_init ( &context, key ) ) != 0 )
                goto err_init;
 
        /* Create space for encoded digest and signature */
        if ( ( rc = asn1_grow ( signature, context.max_len ) ) != 0 )
                goto err_grow;
 
        /* Encode digest */
        if ( ( rc = encode ( &context, digest, value, NULL,
                             signature->data ) ) != 0 )
                goto err_encode;
 
        /* Encipher the encoded digest */
        canonical = rsa_cipher ( &context, signature->data, signature->data );
        assert ( canonical );
        DBGC ( &context, "RSA %p signed %s digest:\n", &context, digest->name );
        DBGC_HDA ( &context, 0, signature->data, signature->len );
 
        /* Free context */
        rsa_free ( &context );
 
        return 0;
 
 err_encode:
 err_grow:
        rsa_free ( &context );
 err_init:
        return rc;
}
 
/**
 * Verify signed digest value using RSA
 *
 * @v pubkey            Public-key algorithm
 * @v key               Key
 * @v digest            Digest algorithm
 * @v value             Digest value
 * @v signature         Signature
 * @ret rc              Return status code
 */
static int rsa_verify ( struct pubkey_algorithm *pubkey,
                        const struct asn1_cursor *key,
                        struct digest_algorithm *digest, const void *value,
                        const struct asn1_cursor *signature ) {
        rsa_encode_t *encode = pubkey->priv;
        struct rsa_context context;
        void *temp;
        void *expected;
        void *actual;
        int canonical;
        int rc;
 
        DBGC ( &context, "RSA %p verifying %s digest:\n",
               &context, digest->name );
        DBGC_HDA ( &context, 0, value, digest->digestsize );
        DBGC_HDA ( &context, 0, signature->data, signature->len );
 
        /* Initialise context */
        if ( ( rc = rsa_init ( &context, key ) ) != 0 )
                goto err_init;
 
        /* 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 );
                rc = -ERANGE;
                goto err_sanity;
        }
 
        /* Decipher the signature (using the big integer input buffer
         * as temporary storage)
         */
        temp = context.input0;
        expected = temp;
        canonical = rsa_cipher ( &context, signature->data, expected );
        DBGC ( &context, "RSA %p deciphered signature:\n", &context );
        DBGC_HDA ( &context, 0, expected, context.max_len );
        if ( ! canonical ) {
                DBGC ( &context, "RSA %p signature was not canonical\n",
                       &context );
                rc = -ERANGE;
                goto err_canonical;
        }
 
        /* Encode digest (using the big integer output buffer as
         * temporary storage)
         */
        temp = context.output0;
        actual = temp;
        if ( ( rc = encode ( &context, digest, value, expected,
                             actual ) ) != 0 )
                goto err_encode;
 
        /* Verify the signature */
        if ( memcmp ( actual, expected, context.max_len ) != 0 ) {
                DBGC ( &context, "RSA %p signature verification failed\n",
                       &context );
                rc = -EACCES_VERIFY;
                goto err_verify;
        }
 
        /* Free context */
        rsa_free ( &context );
 
        DBGC ( &context, "RSA %p signature verified successfully\n", &context );
        return 0;
 
 err_verify:
 err_encode:
 err_canonical:
 err_sanity:
        rsa_free ( &context );
 err_init:
        return rc;
}
 
/**
 * Check for matching RSA public/private key pair
 *
 * @v pubkey            Public-key algorithm
 * @v private_key       Private key
 * @v public_key        Public key
 * @ret rc              Return status code
 */
static int rsa_match ( struct pubkey_algorithm *pubkey __unused,
                       const struct asn1_cursor *private_key,
                       const struct asn1_cursor *public_key ) {
        struct asn1_cursor private_modulus;
        struct asn1_cursor private_exponent;
        struct asn1_cursor public_modulus;
        struct asn1_cursor public_exponent;
        int rc;
 
        /* Parse moduli and exponents */
        if ( ( rc = rsa_parse_mod_exp ( &private_modulus, &private_exponent,
                                        private_key ) ) != 0 )
                return rc;
        if ( ( rc = rsa_parse_mod_exp ( &public_modulus, &public_exponent,
                                        public_key ) ) != 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",
        .encrypt        = rsa_pkcs1_encrypt,
        .decrypt        = rsa_pkcs1_decrypt,
        .sign           = rsa_sign,
        .verify         = rsa_verify,
        .match          = rsa_match,
        .priv           = rsa_pkcs1_encode,
};
 
/** RSA-PSS public-key algorithm */
struct pubkey_algorithm rsa_pss_algorithm = {
        .name           = "rsa_pss",
        .encrypt        = pubkey_null_encrypt,
        .decrypt        = pubkey_null_decrypt,
        .sign           = rsa_sign,
        .verify         = rsa_verify,
        .match          = rsa_match,
        .priv           = rsa_pss_encode,
};
 
/* Drag in objects via rsa_algorithm */
REQUIRING_SYMBOL ( rsa_algorithm );
 
/* Drag in crypto configuration */
REQUIRE_OBJECT ( config_crypto );