library/psa_crypto_rsa.c

/*
 *  PSA RSA layer on top of Mbed TLS crypto
 */
/*
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

#include "common.h"

#if defined(MBEDTLS_PSA_CRYPTO_C)

#include <psa/crypto.h>
#include "psa_crypto_core.h"
#include "psa_crypto_random_impl.h"
#include "psa_crypto_rsa.h"
#include "psa_crypto_hash.h"

#include <stdlib.h>
#include <string.h>
#include "mbedtls/platform.h"

#include <mbedtls/rsa.h>
#include <mbedtls/error.h>
#include <mbedtls/pk.h>
#include <mbedtls/pk_internal.h>

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_CRYPT) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_OAEP) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)

/* Mbed TLS doesn't support non-byte-aligned key sizes (i.e. key sizes
 * that are not a multiple of 8) well. For example, there is only
 * mbedtls_rsa_get_len(), which returns a number of bytes, and no
 * way to return the exact bit size of a key.
 * To keep things simple, reject non-byte-aligned key sizes. */
static psa_status_t psa_check_rsa_key_byte_aligned(
    const mbedtls_rsa_context *rsa)
{
    mbedtls_mpi n;
    psa_status_t status;
    mbedtls_mpi_init(&n);
    status = mbedtls_to_psa_error(
        mbedtls_rsa_export(rsa, &n, NULL, NULL, NULL, NULL));
    if (status == PSA_SUCCESS) {
        if (mbedtls_mpi_bitlen(&n) % 8 != 0) {
            status = PSA_ERROR_NOT_SUPPORTED;
        }
    }
    mbedtls_mpi_free(&n);
    return status;
}

psa_status_t mbedtls_psa_rsa_load_representation(
    psa_key_type_t type, const uint8_t *data, size_t data_length,
    mbedtls_rsa_context **p_rsa)
{
    psa_status_t status;
    mbedtls_pk_context ctx;
    size_t bits;
    mbedtls_pk_init(&ctx);

    /* Parse the data. */
    if (PSA_KEY_TYPE_IS_KEY_PAIR(type)) {
        status = mbedtls_to_psa_error(
            mbedtls_pk_parse_key(&ctx, data, data_length, NULL, 0));
    } else {
        status = mbedtls_to_psa_error(
            mbedtls_pk_parse_public_key(&ctx, data, data_length));
    }
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    /* We have something that the pkparse module recognizes. If it is a
     * valid RSA key, store it. */
    if (mbedtls_pk_get_type(&ctx) != MBEDTLS_PK_RSA) {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    /* The size of an RSA key doesn't have to be a multiple of 8. Mbed TLS
     * supports non-byte-aligned key sizes, but not well. For example,
     * mbedtls_rsa_get_len() returns the key size in bytes, not in bits. */
    bits = PSA_BYTES_TO_BITS(mbedtls_rsa_get_len(mbedtls_pk_rsa(ctx)));
    if (bits > PSA_VENDOR_RSA_MAX_KEY_BITS) {
        status = PSA_ERROR_NOT_SUPPORTED;
        goto exit;
    }
    status = psa_check_rsa_key_byte_aligned(mbedtls_pk_rsa(ctx));
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    /* Copy out the pointer to the RSA context, and reset the PK context
     * such that pk_free doesn't free the RSA context we just grabbed. */
    *p_rsa = mbedtls_pk_rsa(ctx);
    ctx.pk_info = NULL;

exit:
    mbedtls_pk_free(&ctx);
    return status;
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_CRYPT) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_OAEP) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)

psa_status_t mbedtls_psa_rsa_import_key(
    const psa_key_attributes_t *attributes,
    const uint8_t *data, size_t data_length,
    uint8_t *key_buffer, size_t key_buffer_size,
    size_t *key_buffer_length, size_t *bits)
{
    psa_status_t status;
    mbedtls_rsa_context *rsa = NULL;

    /* Parse input */
    status = mbedtls_psa_rsa_load_representation(attributes->core.type,
                                                 data,
                                                 data_length,
                                                 &rsa);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    *bits = (psa_key_bits_t) PSA_BYTES_TO_BITS(mbedtls_rsa_get_len(rsa));

    /* Re-export the data to PSA export format, such that we can store export
     * representation in the key slot. Export representation in case of RSA is
     * the smallest representation that's allowed as input, so a straight-up
     * allocation of the same size as the input buffer will be large enough. */
    status = mbedtls_psa_rsa_export_key(attributes->core.type,
                                        rsa,
                                        key_buffer,
                                        key_buffer_size,
                                        key_buffer_length);
exit:
    /* Always free the RSA object */
    mbedtls_rsa_free(rsa);
    mbedtls_free(rsa);

    return status;
}

psa_status_t mbedtls_psa_rsa_export_key(psa_key_type_t type,
                                        mbedtls_rsa_context *rsa,
                                        uint8_t *data,
                                        size_t data_size,
                                        size_t *data_length)
{
#if defined(MBEDTLS_PK_WRITE_C)
    int ret;
    mbedtls_pk_context pk;
    uint8_t *pos = data + data_size;

    mbedtls_pk_init(&pk);
    pk.pk_info = &mbedtls_rsa_info;
    pk.pk_ctx = rsa;

    /* PSA Crypto API defines the format of an RSA key as a DER-encoded
     * representation of the non-encrypted PKCS#1 RSAPrivateKey for a
     * private key and of the RFC3279 RSAPublicKey for a public key. */
    if (PSA_KEY_TYPE_IS_KEY_PAIR(type)) {
        ret = mbedtls_pk_write_key_der(&pk, data, data_size);
    } else {
        ret = mbedtls_pk_write_pubkey(&pos, data, &pk);
    }

    if (ret < 0) {
        /* Clean up in case pk_write failed halfway through. */
        memset(data, 0, data_size);
        return mbedtls_to_psa_error(ret);
    }

    /* The mbedtls_pk_xxx functions write to the end of the buffer.
     * Move the data to the beginning and erase remaining data
     * at the original location. */
    if (2 * (size_t) ret <= data_size) {
        memcpy(data, data + data_size - ret, ret);
        memset(data + data_size - ret, 0, ret);
    } else if ((size_t) ret < data_size) {
        memmove(data, data + data_size - ret, ret);
        memset(data + ret, 0, data_size - ret);
    }

    *data_length = ret;
    return PSA_SUCCESS;
#else
    (void) type;
    (void) rsa;
    (void) data;
    (void) data_size;
    (void) data_length;
    return PSA_ERROR_NOT_SUPPORTED;
#endif /* MBEDTLS_PK_WRITE_C */
}

psa_status_t mbedtls_psa_rsa_export_public_key(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    uint8_t *data, size_t data_size, size_t *data_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;

    status = mbedtls_psa_rsa_load_representation(
        attributes->core.type, key_buffer, key_buffer_size, &rsa);
    if (status != PSA_SUCCESS) {
        return status;
    }

    status = mbedtls_psa_rsa_export_key(PSA_KEY_TYPE_RSA_PUBLIC_KEY,
                                        rsa,
                                        data,
                                        data_size,
                                        data_length);

    mbedtls_rsa_free(rsa);
    mbedtls_free(rsa);

    return status;
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) && \
    defined(MBEDTLS_GENPRIME)
static psa_status_t psa_rsa_read_exponent(const uint8_t *domain_parameters,
                                          size_t domain_parameters_size,
                                          int *exponent)
{
    size_t i;
    uint32_t acc = 0;

    if (domain_parameters_size == 0) {
        *exponent = 65537;
        return PSA_SUCCESS;
    }

    /* Mbed TLS encodes the public exponent as an int. For simplicity, only
     * support values that fit in a 32-bit integer, which is larger than
     * int on just about every platform anyway. */
    if (domain_parameters_size > sizeof(acc)) {
        return PSA_ERROR_NOT_SUPPORTED;
    }
    for (i = 0; i < domain_parameters_size; i++) {
        acc = (acc << 8) | domain_parameters[i];
    }
    if (acc > INT_MAX) {
        return PSA_ERROR_NOT_SUPPORTED;
    }
    *exponent = acc;
    return PSA_SUCCESS;
}

psa_status_t mbedtls_psa_rsa_generate_key(
    const psa_key_attributes_t *attributes,
    uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length)
{
    psa_status_t status;
    mbedtls_rsa_context rsa;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    int exponent;

    status = psa_rsa_read_exponent(attributes->domain_parameters,
                                   attributes->domain_parameters_size,
                                   &exponent);
    if (status != PSA_SUCCESS) {
        return status;
    }

    mbedtls_rsa_init(&rsa, MBEDTLS_RSA_PKCS_V15, MBEDTLS_MD_NONE);
    ret = mbedtls_rsa_gen_key(&rsa,
                              mbedtls_psa_get_random,
                              MBEDTLS_PSA_RANDOM_STATE,
                              (unsigned int) attributes->core.bits,
                              exponent);
    if (ret != 0) {
        return mbedtls_to_psa_error(ret);
    }

    status = mbedtls_psa_rsa_export_key(attributes->core.type,
                                        &rsa, key_buffer, key_buffer_size,
                                        key_buffer_length);
    mbedtls_rsa_free(&rsa);

    return status;
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR)
        * defined(MBEDTLS_GENPRIME) */

/****************************************************************/
/* Sign/verify hashes */
/****************************************************************/

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)

/* Decode the hash algorithm from alg and store the mbedtls encoding in
 * md_alg. Verify that the hash length is acceptable. */
static psa_status_t psa_rsa_decode_md_type(psa_algorithm_t alg,
                                           size_t hash_length,
                                           mbedtls_md_type_t *md_alg)
{
    psa_algorithm_t hash_alg = PSA_ALG_SIGN_GET_HASH(alg);
    const mbedtls_md_info_t *md_info = mbedtls_md_info_from_psa(hash_alg);
    *md_alg = mbedtls_md_get_type(md_info);

    /* The Mbed TLS RSA module uses an unsigned int for hash length
     * parameters. Validate that it fits so that we don't risk an
     * overflow later. */
#if SIZE_MAX > UINT_MAX
    if (hash_length > UINT_MAX) {
        return PSA_ERROR_INVALID_ARGUMENT;
    }
#endif

    /* For signatures using a hash, the hash length must be correct. */
    if (alg != PSA_ALG_RSA_PKCS1V15_SIGN_RAW) {
        if (md_info == NULL) {
            return PSA_ERROR_NOT_SUPPORTED;
        }
        if (mbedtls_md_get_size(md_info) != hash_length) {
            return PSA_ERROR_INVALID_ARGUMENT;
        }
    }

    return PSA_SUCCESS;
}

psa_status_t mbedtls_psa_rsa_sign_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    uint8_t *signature, size_t signature_size, size_t *signature_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_md_type_t md_alg;

    status = mbedtls_psa_rsa_load_representation(attributes->core.type,
                                                 key_buffer,
                                                 key_buffer_size,
                                                 &rsa);
    if (status != PSA_SUCCESS) {
        return status;
    }

    status = psa_rsa_decode_md_type(alg, hash_length, &md_alg);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    if (signature_size < mbedtls_rsa_get_len(rsa)) {
        status = PSA_ERROR_BUFFER_TOO_SMALL;
        goto exit;
    }

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN)
    if (PSA_ALG_IS_RSA_PKCS1V15_SIGN(alg)) {
        mbedtls_rsa_set_padding(rsa, MBEDTLS_RSA_PKCS_V15,
                                MBEDTLS_MD_NONE);
        ret = mbedtls_rsa_pkcs1_sign(rsa,
                                     mbedtls_psa_get_random,
                                     MBEDTLS_PSA_RANDOM_STATE,
                                     MBEDTLS_RSA_PRIVATE,
                                     md_alg,
                                     (unsigned int) hash_length,
                                     hash,
                                     signature);
    } else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN */
#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
    if (PSA_ALG_IS_RSA_PSS(alg)) {
        mbedtls_rsa_set_padding(rsa, MBEDTLS_RSA_PKCS_V21, md_alg);
        ret = mbedtls_rsa_rsassa_pss_sign(rsa,
                                          mbedtls_psa_get_random,
                                          MBEDTLS_PSA_RANDOM_STATE,
                                          MBEDTLS_RSA_PRIVATE,
                                          MBEDTLS_MD_NONE,
                                          (unsigned int) hash_length,
                                          hash,
                                          signature);
    } else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */
    {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    if (ret == 0) {
        *signature_length = mbedtls_rsa_get_len(rsa);
    }
    status = mbedtls_to_psa_error(ret);

exit:
    mbedtls_rsa_free(rsa);
    mbedtls_free(rsa);

    return status;
}

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
static int rsa_pss_expected_salt_len(psa_algorithm_t alg,
                                     const mbedtls_rsa_context *rsa,
                                     size_t hash_length)
{
    if (PSA_ALG_IS_RSA_PSS_ANY_SALT(alg)) {
        return MBEDTLS_RSA_SALT_LEN_ANY;
    }
    /* Otherwise: standard salt length, i.e. largest possible salt length
     * up to the hash length. */
    int klen = (int) mbedtls_rsa_get_len(rsa);   // known to fit
    int hlen = (int) hash_length; // known to fit
    int room = klen - 2 - hlen;
    if (room < 0) {
        return 0;  // there is no valid signature in this case anyway
    } else if (room > hlen) {
        return hlen;
    } else {
        return room;
    }
}
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */

psa_status_t mbedtls_psa_rsa_verify_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    const uint8_t *signature, size_t signature_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_md_type_t md_alg;

    status = mbedtls_psa_rsa_load_representation(attributes->core.type,
                                                 key_buffer,
                                                 key_buffer_size,
                                                 &rsa);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    status = psa_rsa_decode_md_type(alg, hash_length, &md_alg);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    if (signature_length != mbedtls_rsa_get_len(rsa)) {
        status = PSA_ERROR_INVALID_SIGNATURE;
        goto exit;
    }

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN)
    if (PSA_ALG_IS_RSA_PKCS1V15_SIGN(alg)) {
        mbedtls_rsa_set_padding(rsa, MBEDTLS_RSA_PKCS_V15,
                                MBEDTLS_MD_NONE);
        ret = mbedtls_rsa_pkcs1_verify(rsa,
                                       mbedtls_psa_get_random,
                                       MBEDTLS_PSA_RANDOM_STATE,
                                       MBEDTLS_RSA_PUBLIC,
                                       md_alg,
                                       (unsigned int) hash_length,
                                       hash,
                                       signature);
    } else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN */
#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
    if (PSA_ALG_IS_RSA_PSS(alg)) {
        int slen = rsa_pss_expected_salt_len(alg, rsa, hash_length);
        mbedtls_rsa_set_padding(rsa, MBEDTLS_RSA_PKCS_V21, md_alg);
        ret = mbedtls_rsa_rsassa_pss_verify_ext(rsa,
                                                mbedtls_psa_get_random,
                                                MBEDTLS_PSA_RANDOM_STATE,
                                                MBEDTLS_RSA_PUBLIC,
                                                md_alg,
                                                (unsigned int) hash_length,
                                                hash,
                                                md_alg,
                                                slen,
                                                signature);
    } else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */
    {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    /* Mbed TLS distinguishes "invalid padding" from "valid padding but
     * the rest of the signature is invalid". This has little use in
     * practice and PSA doesn't report this distinction. */
    status = (ret == MBEDTLS_ERR_RSA_INVALID_PADDING) ?
             PSA_ERROR_INVALID_SIGNATURE :
             mbedtls_to_psa_error(ret);

exit:
    mbedtls_rsa_free(rsa);
    mbedtls_free(rsa);

    return status;
}

#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) */

#endif /* MBEDTLS_PSA_CRYPTO_C */