/* $OpenBSD: ssh-rsa.c,v 1.79 2023/03/05 05:34:09 dtucker Exp $ */
/*
 * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include "includes.h"

#ifdef WITH_OPENSSL

#include <sys/types.h>

#include <openssl/evp.h>
#include <openssl/err.h>

#include <stdarg.h>
#include <string.h>

#include "sshbuf.h"
#include "ssherr.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"
#include "digest.h"
#include "log.h"

#include "openbsd-compat/openssl-compat.h"

static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);

static u_int
ssh_rsa_size(const struct sshkey *key)
{
        const BIGNUM *rsa_n;

        if (key->rsa == NULL)
                return 0;
        RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
        return BN_num_bits(rsa_n);
}

static int
ssh_rsa_alloc(struct sshkey *k)
{
        if ((k->rsa = RSA_new()) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        return 0;
}

static void
ssh_rsa_cleanup(struct sshkey *k)
{
        RSA_free(k->rsa);
        k->rsa = NULL;
}

static int
ssh_rsa_equal(const struct sshkey *a, const struct sshkey *b)
{
        const BIGNUM *rsa_e_a, *rsa_n_a;
        const BIGNUM *rsa_e_b, *rsa_n_b;

        if (a->rsa == NULL || b->rsa == NULL)
                return 0;
        RSA_get0_key(a->rsa, &rsa_n_a, &rsa_e_a, NULL);
        RSA_get0_key(b->rsa, &rsa_n_b, &rsa_e_b, NULL);
        if (rsa_e_a == NULL || rsa_e_b == NULL)
                return 0;
        if (rsa_n_a == NULL || rsa_n_b == NULL)
                return 0;
        if (BN_cmp(rsa_e_a, rsa_e_b) != 0)
                return 0;
        if (BN_cmp(rsa_n_a, rsa_n_b) != 0)
                return 0;
        return 1;
}

static int
ssh_rsa_serialize_public(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
        int r;
        const BIGNUM *rsa_n, *rsa_e;

        if (key->rsa == NULL)
                return SSH_ERR_INVALID_ARGUMENT;
        RSA_get0_key(key->rsa, &rsa_n, &rsa_e, NULL);
        if ((r = sshbuf_put_bignum2(b, rsa_e)) != 0 ||
            (r = sshbuf_put_bignum2(b, rsa_n)) != 0)
                return r;

        return 0;
}

static int
ssh_rsa_serialize_private(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
        int r;
        const BIGNUM *rsa_n, *rsa_e, *rsa_d, *rsa_iqmp, *rsa_p, *rsa_q;

        RSA_get0_key(key->rsa, &rsa_n, &rsa_e, &rsa_d);
        RSA_get0_factors(key->rsa, &rsa_p, &rsa_q);
        RSA_get0_crt_params(key->rsa, NULL, NULL, &rsa_iqmp);

        if (!sshkey_is_cert(key)) {
                /* Note: can't reuse ssh_rsa_serialize_public: e, n vs. n, e */
                if ((r = sshbuf_put_bignum2(b, rsa_n)) != 0 ||
                    (r = sshbuf_put_bignum2(b, rsa_e)) != 0)
                        return r;
        }
        if ((r = sshbuf_put_bignum2(b, rsa_d)) != 0 ||
            (r = sshbuf_put_bignum2(b, rsa_iqmp)) != 0 ||
            (r = sshbuf_put_bignum2(b, rsa_p)) != 0 ||
            (r = sshbuf_put_bignum2(b, rsa_q)) != 0)
                return r;

        return 0;
}

static int
ssh_rsa_generate(struct sshkey *k, int bits)
{
        RSA *private = NULL;
        BIGNUM *f4 = NULL;
        int ret = SSH_ERR_INTERNAL_ERROR;

        if (bits < SSH_RSA_MINIMUM_MODULUS_SIZE ||
            bits > SSHBUF_MAX_BIGNUM * 8)
                return SSH_ERR_KEY_LENGTH;
        if ((private = RSA_new()) == NULL || (f4 = BN_new()) == NULL) {
                ret = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        if (!BN_set_word(f4, RSA_F4) ||
            !RSA_generate_key_ex(private, bits, f4, NULL)) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        k->rsa = private;
        private = NULL;
        ret = 0;
 out:
        RSA_free(private);
        BN_free(f4);
        return ret;
}

static int
ssh_rsa_copy_public(const struct sshkey *from, struct sshkey *to)
{
        const BIGNUM *rsa_n, *rsa_e;
        BIGNUM *rsa_n_dup = NULL, *rsa_e_dup = NULL;
        int r = SSH_ERR_INTERNAL_ERROR;

        RSA_get0_key(from->rsa, &rsa_n, &rsa_e, NULL);
        if ((rsa_n_dup = BN_dup(rsa_n)) == NULL ||
            (rsa_e_dup = BN_dup(rsa_e)) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        if (!RSA_set0_key(to->rsa, rsa_n_dup, rsa_e_dup, NULL)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        rsa_n_dup = rsa_e_dup = NULL; /* transferred */
        /* success */
        r = 0;
 out:
        BN_clear_free(rsa_n_dup);
        BN_clear_free(rsa_e_dup);
        return r;
}

static int
ssh_rsa_deserialize_public(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
        int ret = SSH_ERR_INTERNAL_ERROR;
        BIGNUM *rsa_n = NULL, *rsa_e = NULL;

        if (sshbuf_get_bignum2(b, &rsa_e) != 0 ||
            sshbuf_get_bignum2(b, &rsa_n) != 0) {
                ret = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if (!RSA_set0_key(key->rsa, rsa_n, rsa_e, NULL)) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        rsa_n = rsa_e = NULL; /* transferred */
        if ((ret = sshkey_check_rsa_length(key, 0)) != 0)
                goto out;
#ifdef DEBUG_PK
        RSA_print_fp(stderr, key->rsa, 8);
#endif
        /* success */
        ret = 0;
 out:
        BN_clear_free(rsa_n);
        BN_clear_free(rsa_e);
        return ret;
}

static int
ssh_rsa_deserialize_private(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
        int r;
        BIGNUM *rsa_n = NULL, *rsa_e = NULL, *rsa_d = NULL;
        BIGNUM *rsa_iqmp = NULL, *rsa_p = NULL, *rsa_q = NULL;

        /* Note: can't reuse ssh_rsa_deserialize_public: e, n vs. n, e */
        if (!sshkey_is_cert(key)) {
                if ((r = sshbuf_get_bignum2(b, &rsa_n)) != 0 ||
                    (r = sshbuf_get_bignum2(b, &rsa_e)) != 0)
                        goto out;
                if (!RSA_set0_key(key->rsa, rsa_n, rsa_e, NULL)) {
                        r = SSH_ERR_LIBCRYPTO_ERROR;
                        goto out;
                }
                rsa_n = rsa_e = NULL; /* transferred */
        }
        if ((r = sshbuf_get_bignum2(b, &rsa_d)) != 0 ||
            (r = sshbuf_get_bignum2(b, &rsa_iqmp)) != 0 ||
            (r = sshbuf_get_bignum2(b, &rsa_p)) != 0 ||
            (r = sshbuf_get_bignum2(b, &rsa_q)) != 0)
                goto out;
        if (!RSA_set0_key(key->rsa, NULL, NULL, rsa_d)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        rsa_d = NULL; /* transferred */
        if (!RSA_set0_factors(key->rsa, rsa_p, rsa_q)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        rsa_p = rsa_q = NULL; /* transferred */
        if ((r = sshkey_check_rsa_length(key, 0)) != 0)
                goto out;
        if ((r = ssh_rsa_complete_crt_parameters(key, rsa_iqmp)) != 0)
                goto out;
        if (RSA_blinding_on(key->rsa, NULL) != 1) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        /* success */
        r = 0;
 out:
        BN_clear_free(rsa_n);
        BN_clear_free(rsa_e);
        BN_clear_free(rsa_d);
        BN_clear_free(rsa_p);
        BN_clear_free(rsa_q);
        BN_clear_free(rsa_iqmp);
        return r;
}

static const char *
rsa_hash_alg_ident(int hash_alg)
{
        switch (hash_alg) {
        case SSH_DIGEST_SHA1:
                return "ssh-rsa";
        case SSH_DIGEST_SHA256:
                return "rsa-sha2-256";
        case SSH_DIGEST_SHA512:
                return "rsa-sha2-512";
        }
        return NULL;
}

/*
 * Returns the hash algorithm ID for a given algorithm identifier as used
 * inside the signature blob,
 */
static int
rsa_hash_id_from_ident(const char *ident)
{
        if (strcmp(ident, "ssh-rsa") == 0)
                return SSH_DIGEST_SHA1;
        if (strcmp(ident, "rsa-sha2-256") == 0)
                return SSH_DIGEST_SHA256;
        if (strcmp(ident, "rsa-sha2-512") == 0)
                return SSH_DIGEST_SHA512;
        return -1;
}

/*
 * Return the hash algorithm ID for the specified key name. This includes
 * all the cases of rsa_hash_id_from_ident() but also the certificate key
 * types.
 */
static int
rsa_hash_id_from_keyname(const char *alg)
{
        int r;

        if ((r = rsa_hash_id_from_ident(alg)) != -1)
                return r;
        if (strcmp(alg, "ssh-rsa-cert-v01@openssh.com") == 0)
                return SSH_DIGEST_SHA1;
        if (strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0)
                return SSH_DIGEST_SHA256;
        if (strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0)
                return SSH_DIGEST_SHA512;
        return -1;
}

static int
rsa_hash_alg_nid(int type)
{
        switch (type) {
        case SSH_DIGEST_SHA1:
                return NID_sha1;
        case SSH_DIGEST_SHA256:
                return NID_sha256;
        case SSH_DIGEST_SHA512:
                return NID_sha512;
        default:
                return -1;
        }
}

int
ssh_rsa_complete_crt_parameters(struct sshkey *key, const BIGNUM *iqmp)
{
        const BIGNUM *rsa_p, *rsa_q, *rsa_d;
        BIGNUM *aux = NULL, *d_consttime = NULL;
        BIGNUM *rsa_dmq1 = NULL, *rsa_dmp1 = NULL, *rsa_iqmp = NULL;
        BN_CTX *ctx = NULL;
        int r;

        if (key == NULL || key->rsa == NULL ||
            sshkey_type_plain(key->type) != KEY_RSA)
                return SSH_ERR_INVALID_ARGUMENT;

        RSA_get0_key(key->rsa, NULL, NULL, &rsa_d);
        RSA_get0_factors(key->rsa, &rsa_p, &rsa_q);

        if ((ctx = BN_CTX_new()) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        if ((aux = BN_new()) == NULL ||
            (rsa_dmq1 = BN_new()) == NULL ||
            (rsa_dmp1 = BN_new()) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        if ((d_consttime = BN_dup(rsa_d)) == NULL ||
            (rsa_iqmp = BN_dup(iqmp)) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        BN_set_flags(aux, BN_FLG_CONSTTIME);
        BN_set_flags(d_consttime, BN_FLG_CONSTTIME);

        if ((BN_sub(aux, rsa_q, BN_value_one()) == 0) ||
            (BN_mod(rsa_dmq1, d_consttime, aux, ctx) == 0) ||
            (BN_sub(aux, rsa_p, BN_value_one()) == 0) ||
            (BN_mod(rsa_dmp1, d_consttime, aux, ctx) == 0)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        if (!RSA_set0_crt_params(key->rsa, rsa_dmp1, rsa_dmq1, rsa_iqmp)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        rsa_dmp1 = rsa_dmq1 = rsa_iqmp = NULL; /* transferred */
        /* success */
        r = 0;
 out:
        BN_clear_free(aux);
        BN_clear_free(d_consttime);
        BN_clear_free(rsa_dmp1);
        BN_clear_free(rsa_dmq1);
        BN_clear_free(rsa_iqmp);
        BN_CTX_free(ctx);
        return r;
}

/* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
static int
ssh_rsa_sign(struct sshkey *key,
    u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen,
    const char *alg, const char *sk_provider, const char *sk_pin, u_int compat)
{
        const BIGNUM *rsa_n;
        u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
        size_t slen = 0;
        u_int hlen, len;
        int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
        struct sshbuf *b = NULL;

        if (lenp != NULL)
                *lenp = 0;
        if (sigp != NULL)
                *sigp = NULL;

        if (alg == NULL || strlen(alg) == 0)
                hash_alg = SSH_DIGEST_SHA1;
        else
                hash_alg = rsa_hash_id_from_keyname(alg);
        if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
            sshkey_type_plain(key->type) != KEY_RSA)
                return SSH_ERR_INVALID_ARGUMENT;
        RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
        if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
                return SSH_ERR_KEY_LENGTH;
        slen = RSA_size(key->rsa);
        if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
                return SSH_ERR_INVALID_ARGUMENT;

        /* hash the data */
        nid = rsa_hash_alg_nid(hash_alg);
        if ((hlen = ssh_digest_bytes(hash_alg)) == 0)
                return SSH_ERR_INTERNAL_ERROR;
        if ((ret = ssh_digest_memory(hash_alg, data, datalen,
            digest, sizeof(digest))) != 0)
                goto out;

        if ((sig = malloc(slen)) == NULL) {
                ret = SSH_ERR_ALLOC_FAIL;
                goto out;
        }

        if (RSA_sign(nid, digest, hlen, sig, &len, key->rsa) != 1) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        if (len < slen) {
                size_t diff = slen - len;
                memmove(sig + diff, sig, len);
                explicit_bzero(sig, diff);
        } else if (len > slen) {
                ret = SSH_ERR_INTERNAL_ERROR;
                goto out;
        }
        /* encode signature */
        if ((b = sshbuf_new()) == NULL) {
                ret = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 ||
            (ret = sshbuf_put_string(b, sig, slen)) != 0)
                goto out;
        len = sshbuf_len(b);
        if (sigp != NULL) {
                if ((*sigp = malloc(len)) == NULL) {
                        ret = SSH_ERR_ALLOC_FAIL;
                        goto out;
                }
                memcpy(*sigp, sshbuf_ptr(b), len);
        }
        if (lenp != NULL)
                *lenp = len;
        ret = 0;
 out:
        explicit_bzero(digest, sizeof(digest));
        freezero(sig, slen);
        sshbuf_free(b);
        return ret;
}

static int
ssh_rsa_verify(const struct sshkey *key,
    const u_char *sig, size_t siglen,
    const u_char *data, size_t dlen, const char *alg, u_int compat,
    struct sshkey_sig_details **detailsp)
{
        const BIGNUM *rsa_n;
        char *sigtype = NULL;
        int hash_alg, want_alg, ret = SSH_ERR_INTERNAL_ERROR;
        size_t len = 0, diff, modlen, hlen;
        struct sshbuf *b = NULL;
        u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;

        if (key == NULL || key->rsa == NULL ||
            sshkey_type_plain(key->type) != KEY_RSA ||
            sig == NULL || siglen == 0)
                return SSH_ERR_INVALID_ARGUMENT;
        RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
        if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
                return SSH_ERR_KEY_LENGTH;

        if ((b = sshbuf_from(sig, siglen)) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        if (sshbuf_get_cstring(b, &sigtype, NULL) != 0) {
                ret = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if ((hash_alg = rsa_hash_id_from_ident(sigtype)) == -1) {
                ret = SSH_ERR_KEY_TYPE_MISMATCH;
                goto out;
        }
        /*
         * Allow ssh-rsa-cert-v01 certs to generate SHA2 signatures for
         * legacy reasons, but otherwise the signature type should match.
         */
        if (alg != NULL && strcmp(alg, "ssh-rsa-cert-v01@openssh.com") != 0) {
                if ((want_alg = rsa_hash_id_from_keyname(alg)) == -1) {
                        ret = SSH_ERR_INVALID_ARGUMENT;
                        goto out;
                }
                if (hash_alg != want_alg) {
                        ret = SSH_ERR_SIGNATURE_INVALID;
                        goto out;
                }
        }
        if (sshbuf_get_string(b, &sigblob, &len) != 0) {
                ret = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if (sshbuf_len(b) != 0) {
                ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
                goto out;
        }
        /* RSA_verify expects a signature of RSA_size */
        modlen = RSA_size(key->rsa);
        if (len > modlen) {
                ret = SSH_ERR_KEY_BITS_MISMATCH;
                goto out;
        } else if (len < modlen) {
                diff = modlen - len;
                osigblob = sigblob;
                if ((sigblob = realloc(sigblob, modlen)) == NULL) {
                        sigblob = osigblob; /* put it back for clear/free */
                        ret = SSH_ERR_ALLOC_FAIL;
                        goto out;
                }
                memmove(sigblob + diff, sigblob, len);
                explicit_bzero(sigblob, diff);
                len = modlen;
        }
        if ((hlen = ssh_digest_bytes(hash_alg)) == 0) {
                ret = SSH_ERR_INTERNAL_ERROR;
                goto out;
        }
        if ((ret = ssh_digest_memory(hash_alg, data, dlen,
            digest, sizeof(digest))) != 0)
                goto out;

        ret = openssh_RSA_verify(hash_alg, digest, hlen, sigblob, len,
            key->rsa);
 out:
        freezero(sigblob, len);
        free(sigtype);
        sshbuf_free(b);
        explicit_bzero(digest, sizeof(digest));
        return ret;
}

/*
 * See:
 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 */

/*
 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 *      oiw(14) secsig(3) algorithms(2) 26 }
 */
static const u_char id_sha1[] = {
        0x30, 0x21, /* type Sequence, length 0x21 (33) */
        0x30, 0x09, /* type Sequence, length 0x09 */
        0x06, 0x05, /* type OID, length 0x05 */
        0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
        0x05, 0x00, /* NULL */
        0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
};

/*
 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
 * id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
 *      organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
 *      id-sha256(1) }
 */
static const u_char id_sha256[] = {
        0x30, 0x31, /* type Sequence, length 0x31 (49) */
        0x30, 0x0d, /* type Sequence, length 0x0d (13) */
        0x06, 0x09, /* type OID, length 0x09 */
        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */
        0x05, 0x00, /* NULL */
        0x04, 0x20  /* Octet string, length 0x20 (32), followed by sha256 hash */
};

/*
 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
 * id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
 *      organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
 *      id-sha256(3) }
 */
static const u_char id_sha512[] = {
        0x30, 0x51, /* type Sequence, length 0x51 (81) */
        0x30, 0x0d, /* type Sequence, length 0x0d (13) */
        0x06, 0x09, /* type OID, length 0x09 */
        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */
        0x05, 0x00, /* NULL */
        0x04, 0x40  /* Octet string, length 0x40 (64), followed by sha512 hash */
};

static int
rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp)
{
        switch (hash_alg) {
        case SSH_DIGEST_SHA1:
                *oidp = id_sha1;
                *oidlenp = sizeof(id_sha1);
                break;
        case SSH_DIGEST_SHA256:
                *oidp = id_sha256;
                *oidlenp = sizeof(id_sha256);
                break;
        case SSH_DIGEST_SHA512:
                *oidp = id_sha512;
                *oidlenp = sizeof(id_sha512);
                break;
        default:
                return SSH_ERR_INVALID_ARGUMENT;
        }
        return 0;
}

static int
openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
    u_char *sigbuf, size_t siglen, RSA *rsa)
{
        size_t rsasize = 0, oidlen = 0, hlen = 0;
        int ret, len, oidmatch, hashmatch;
        const u_char *oid = NULL;
        u_char *decrypted = NULL;

        if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0)
                return ret;
        ret = SSH_ERR_INTERNAL_ERROR;
        hlen = ssh_digest_bytes(hash_alg);
        if (hashlen != hlen) {
                ret = SSH_ERR_INVALID_ARGUMENT;
                goto done;
        }
        rsasize = RSA_size(rsa);
        if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
            siglen == 0 || siglen > rsasize) {
                ret = SSH_ERR_INVALID_ARGUMENT;
                goto done;
        }
        if ((decrypted = malloc(rsasize)) == NULL) {
                ret = SSH_ERR_ALLOC_FAIL;
                goto done;
        }
        if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
            RSA_PKCS1_PADDING)) < 0) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto done;
        }
        if (len < 0 || (size_t)len != hlen + oidlen) {
                ret = SSH_ERR_INVALID_FORMAT;
                goto done;
        }
        oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
        hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
        if (!oidmatch || !hashmatch) {
                ret = SSH_ERR_SIGNATURE_INVALID;
                goto done;
        }
        ret = 0;
done:
        freezero(decrypted, rsasize);
        return ret;
}

static const struct sshkey_impl_funcs sshkey_rsa_funcs = {
        /* .size = */           ssh_rsa_size,
        /* .alloc = */          ssh_rsa_alloc,
        /* .cleanup = */        ssh_rsa_cleanup,
        /* .equal = */          ssh_rsa_equal,
        /* .ssh_serialize_public = */ ssh_rsa_serialize_public,
        /* .ssh_deserialize_public = */ ssh_rsa_deserialize_public,
        /* .ssh_serialize_private = */ ssh_rsa_serialize_private,
        /* .ssh_deserialize_private = */ ssh_rsa_deserialize_private,
        /* .generate = */       ssh_rsa_generate,
        /* .copy_public = */    ssh_rsa_copy_public,
        /* .sign = */           ssh_rsa_sign,
        /* .verify = */         ssh_rsa_verify,
};

const struct sshkey_impl sshkey_rsa_impl = {
        /* .name = */           "ssh-rsa",
        /* .shortname = */      "RSA",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_RSA,
        /* .nid = */            0,
        /* .cert = */           0,
        /* .sigonly = */        0,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};

const struct sshkey_impl sshkey_rsa_cert_impl = {
        /* .name = */           "ssh-rsa-cert-v01@openssh.com",
        /* .shortname = */      "RSA-CERT",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_RSA_CERT,
        /* .nid = */            0,
        /* .cert = */           1,
        /* .sigonly = */        0,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};

/* SHA2 signature algorithms */

const struct sshkey_impl sshkey_rsa_sha256_impl = {
        /* .name = */           "rsa-sha2-256",
        /* .shortname = */      "RSA",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_RSA,
        /* .nid = */            0,
        /* .cert = */           0,
        /* .sigonly = */        1,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};

const struct sshkey_impl sshkey_rsa_sha512_impl = {
        /* .name = */           "rsa-sha2-512",
        /* .shortname = */      "RSA",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_RSA,
        /* .nid = */            0,
        /* .cert = */           0,
        /* .sigonly = */        1,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};

const struct sshkey_impl sshkey_rsa_sha256_cert_impl = {
        /* .name = */           "rsa-sha2-256-cert-v01@openssh.com",
        /* .shortname = */      "RSA-CERT",
        /* .sigalg = */         "rsa-sha2-256",
        /* .type = */           KEY_RSA_CERT,
        /* .nid = */            0,
        /* .cert = */           1,
        /* .sigonly = */        1,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};

const struct sshkey_impl sshkey_rsa_sha512_cert_impl = {
        /* .name = */           "rsa-sha2-512-cert-v01@openssh.com",
        /* .shortname = */      "RSA-CERT",
        /* .sigalg = */         "rsa-sha2-512",
        /* .type = */           KEY_RSA_CERT,
        /* .nid = */            0,
        /* .cert = */           1,
        /* .sigonly = */        1,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_rsa_funcs,
};
#endif /* WITH_OPENSSL */