rsa_eay.c

Go to the documentation of this file.

/* crypto/rsa/rsa_eay.c */
/* Copyright (C) 1995-1998 Eric Young ([email protected])
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young ([email protected]).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson ([email protected]).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young ([email protected])"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson ([email protected])"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */
/* ====================================================================
 * Copyright (c) 1998-2006 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    [email protected].
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * ([email protected]).  This product includes software written by Tim
 * Hudson ([email protected]).
 *
 */

#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>

#ifndef RSA_NULL

static int RSA_eay_public_encrypt(int flen, const unsigned char *from,
        unsigned char *to, RSA *rsa,int padding);
static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
        unsigned char *to, RSA *rsa,int padding);
static int RSA_eay_public_decrypt(int flen, const unsigned char *from,
        unsigned char *to, RSA *rsa,int padding);
static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
        unsigned char *to, RSA *rsa,int padding);
static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *i, RSA *rsa, BN_CTX *ctx);
static int RSA_eay_init(RSA *rsa);
static int RSA_eay_finish(RSA *rsa);
static RSA_METHOD rsa_pkcs1_eay_meth={
    "Eric Young's PKCS#1 RSA",
    RSA_eay_public_encrypt,
    RSA_eay_public_decrypt, /* signature verification */
    RSA_eay_private_encrypt, /* signing */
    RSA_eay_private_decrypt,
    RSA_eay_mod_exp,
    BN_mod_exp_mont, /* XXX probably we should not use Montgomery if  e == 3 */
    RSA_eay_init,
    RSA_eay_finish,
    0, /* flags */
    NULL,
    0, /* rsa_sign */
    0, /* rsa_verify */
    NULL /* rsa_keygen */
    };

const RSA_METHOD *RSA_PKCS1_SSLeay(void)
    {
    return(&rsa_pkcs1_eay_meth);
    }

static int RSA_eay_public_encrypt(int flen, const unsigned char *from,
         unsigned char *to, RSA *rsa, int padding)
    {
    BIGNUM *f,*ret;
    int i,j,k,num=0,r= -1;
    unsigned char *buf=NULL;
    BN_CTX *ctx=NULL;

    if (BN_num_bits(rsa->n) > OPENSSL_RSA_MAX_MODULUS_BITS)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT, RSA_R_MODULUS_TOO_LARGE);
        return -1;
        }

    if (BN_ucmp(rsa->n, rsa->e) <= 0)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT, RSA_R_BAD_E_VALUE);
        return -1;
        }

    /* for large moduli, enforce exponent limit */
    if (BN_num_bits(rsa->n) > OPENSSL_RSA_SMALL_MODULUS_BITS)
        {
        if (BN_num_bits(rsa->e) > OPENSSL_RSA_MAX_PUBEXP_BITS)
            {
            RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT, RSA_R_BAD_E_VALUE);
            return -1;
            }
        }
    
    if ((ctx=BN_CTX_new()) == NULL) goto err;
    BN_CTX_start(ctx);
    f = BN_CTX_get(ctx);
    ret = BN_CTX_get(ctx);
    num=BN_num_bytes(rsa->n);
    buf = OPENSSL_malloc(num);
    if (!f || !ret || !buf)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT,ERR_R_MALLOC_FAILURE);
        goto err;
        }

    switch (padding)
        {
    case RSA_PKCS1_PADDING:
        i=RSA_padding_add_PKCS1_type_2(buf,num,from,flen);
        break;
#ifndef OPENSSL_NO_SHA
    case RSA_PKCS1_OAEP_PADDING:
            i=RSA_padding_add_PKCS1_OAEP(buf,num,from,flen,NULL,0);
        break;
#endif
    case RSA_SSLV23_PADDING:
        i=RSA_padding_add_SSLv23(buf,num,from,flen);
        break;
    case RSA_NO_PADDING:
        i=RSA_padding_add_none(buf,num,from,flen);
        break;
    default:
        RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT,RSA_R_UNKNOWN_PADDING_TYPE);
        goto err;
        }
    if (i <= 0) goto err;

    if (BN_bin2bn(buf,num,f) == NULL) goto err;
    
    if (BN_ucmp(f, rsa->n) >= 0)
        {
        /* usually the padding functions would catch this */
        RSAerr(RSA_F_RSA_EAY_PUBLIC_ENCRYPT,RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
        goto err;
        }

    if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
        if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, CRYPTO_LOCK_RSA, rsa->n, ctx))
            goto err;

    if (!rsa->meth->bn_mod_exp(ret,f,rsa->e,rsa->n,ctx,
        rsa->_method_mod_n)) goto err;

    /* put in leading 0 bytes if the number is less than the
     * length of the modulus */
    j=BN_num_bytes(ret);
    i=BN_bn2bin(ret,&(to[num-j]));
    for (k=0; k<(num-i); k++)
        to[k]=0;

    r=num;
err:
    if (ctx != NULL)
        {
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        }
    if (buf != NULL) 
        {
        OPENSSL_cleanse(buf,num);
        OPENSSL_free(buf);
        }
    return(r);
    }

static BN_BLINDING *rsa_get_blinding(RSA *rsa, int *local, BN_CTX *ctx)
{
    BN_BLINDING *ret;
    int got_write_lock = 0;
    CRYPTO_THREADID cur;

    CRYPTO_r_lock(CRYPTO_LOCK_RSA);

    if (rsa->blinding == NULL)
        {
        CRYPTO_r_unlock(CRYPTO_LOCK_RSA);
        CRYPTO_w_lock(CRYPTO_LOCK_RSA);
        got_write_lock = 1;

        if (rsa->blinding == NULL)
            rsa->blinding = RSA_setup_blinding(rsa, ctx);
        }

    ret = rsa->blinding;
    if (ret == NULL)
        goto err;

    CRYPTO_THREADID_current(&cur);
    if (!CRYPTO_THREADID_cmp(&cur, BN_BLINDING_thread_id(ret)))
        {
        /* rsa->blinding is ours! */

        *local = 1;
        }
    else
        {
        /* resort to rsa->mt_blinding instead */

        *local = 0; /* instructs rsa_blinding_convert(), rsa_blinding_invert()
                     * that the BN_BLINDING is shared, meaning that accesses
                     * require locks, and that the blinding factor must be
                     * stored outside the BN_BLINDING
                     */

        if (rsa->mt_blinding == NULL)
            {
            if (!got_write_lock)
                {
                CRYPTO_r_unlock(CRYPTO_LOCK_RSA);
                CRYPTO_w_lock(CRYPTO_LOCK_RSA);
                got_write_lock = 1;
                }
            
            if (rsa->mt_blinding == NULL)
                rsa->mt_blinding = RSA_setup_blinding(rsa, ctx);
            }
        ret = rsa->mt_blinding;
        }

 err:
    if (got_write_lock)
        CRYPTO_w_unlock(CRYPTO_LOCK_RSA);
    else
        CRYPTO_r_unlock(CRYPTO_LOCK_RSA);
    return ret;
}

static int rsa_blinding_convert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
    BN_CTX *ctx)
    {
    if (unblind == NULL)
        /* Local blinding: store the unblinding factor
         * in BN_BLINDING. */
        return BN_BLINDING_convert_ex(f, NULL, b, ctx);
    else
        {
        /* Shared blinding: store the unblinding factor
         * outside BN_BLINDING. */
        int ret;
        CRYPTO_w_lock(CRYPTO_LOCK_RSA_BLINDING);
        ret = BN_BLINDING_convert_ex(f, unblind, b, ctx);
        CRYPTO_w_unlock(CRYPTO_LOCK_RSA_BLINDING);
        return ret;
        }
    }

static int rsa_blinding_invert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
    BN_CTX *ctx)
    {
    /* For local blinding, unblind is set to NULL, and BN_BLINDING_invert_ex
     * will use the unblinding factor stored in BN_BLINDING.
     * If BN_BLINDING is shared between threads, unblind must be non-null:
     * BN_BLINDING_invert_ex will then use the local unblinding factor,
     * and will only read the modulus from BN_BLINDING.
     * In both cases it's safe to access the blinding without a lock.
     */
    return BN_BLINDING_invert_ex(f, unblind, b, ctx);
    }

/* signing */
static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
         unsigned char *to, RSA *rsa, int padding)
    {
    BIGNUM *f, *ret, *res;
    int i,j,k,num=0,r= -1;
    unsigned char *buf=NULL;
    BN_CTX *ctx=NULL;
    int local_blinding = 0;
    /* Used only if the blinding structure is shared. A non-NULL unblind
     * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
     * the unblinding factor outside the blinding structure. */
    BIGNUM *unblind = NULL;
    BN_BLINDING *blinding = NULL;

    if ((ctx=BN_CTX_new()) == NULL) goto err;
    BN_CTX_start(ctx);
    f   = BN_CTX_get(ctx);
    ret = BN_CTX_get(ctx);
    num = BN_num_bytes(rsa->n);
    buf = OPENSSL_malloc(num);
    if(!f || !ret || !buf)
        {
        RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT,ERR_R_MALLOC_FAILURE);
        goto err;
        }

    switch (padding)
        {
    case RSA_PKCS1_PADDING:
        i=RSA_padding_add_PKCS1_type_1(buf,num,from,flen);
        break;
    case RSA_X931_PADDING:
        i=RSA_padding_add_X931(buf,num,from,flen);
        break;
    case RSA_NO_PADDING:
        i=RSA_padding_add_none(buf,num,from,flen);
        break;
    case RSA_SSLV23_PADDING:
    default:
        RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT,RSA_R_UNKNOWN_PADDING_TYPE);
        goto err;
        }
    if (i <= 0) goto err;

    if (BN_bin2bn(buf,num,f) == NULL) goto err;
    
    if (BN_ucmp(f, rsa->n) >= 0)
        {   
        /* usually the padding functions would catch this */
        RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT,RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
        goto err;
        }

    if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
        {
        blinding = rsa_get_blinding(rsa, &local_blinding, ctx);
        if (blinding == NULL)
            {
            RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, ERR_R_INTERNAL_ERROR);
            goto err;
            }
        }
    
    if (blinding != NULL)
        {
        if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL))
            {
            RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT,ERR_R_MALLOC_FAILURE);
            goto err;
            }
        if (!rsa_blinding_convert(blinding, f, unblind, ctx))
            goto err;
        }

    if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
        ((rsa->p != NULL) &&
        (rsa->q != NULL) &&
        (rsa->dmp1 != NULL) &&
        (rsa->dmq1 != NULL) &&
        (rsa->iqmp != NULL)) )
        { 
        if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx)) goto err;
        }
    else
        {
        BIGNUM local_d;
        BIGNUM *d = NULL;
        
        if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
            {
            BN_init(&local_d);
            d = &local_d;
            BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
            }
        else
            d= rsa->d;

        if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
            if(!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, CRYPTO_LOCK_RSA, rsa->n, ctx))
                goto err;

        if (!rsa->meth->bn_mod_exp(ret,f,d,rsa->n,ctx,
                rsa->_method_mod_n)) goto err;
        }

    if (blinding)
        if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
            goto err;

    if (padding == RSA_X931_PADDING)
        {
        BN_sub(f, rsa->n, ret);
        if (BN_cmp(ret, f))
            res = f;
        else
            res = ret;
        }
    else
        res = ret;

    /* put in leading 0 bytes if the number is less than the
     * length of the modulus */
    j=BN_num_bytes(res);
    i=BN_bn2bin(res,&(to[num-j]));
    for (k=0; k<(num-i); k++)
        to[k]=0;

    r=num;
err:
    if (ctx != NULL)
        {
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        }
    if (buf != NULL)
        {
        OPENSSL_cleanse(buf,num);
        OPENSSL_free(buf);
        }
    return(r);
    }

static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
         unsigned char *to, RSA *rsa, int padding)
    {
    BIGNUM *f, *ret;
    int j,num=0,r= -1;
    unsigned char *p;
    unsigned char *buf=NULL;
    BN_CTX *ctx=NULL;
    int local_blinding = 0;
    /* Used only if the blinding structure is shared. A non-NULL unblind
     * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
     * the unblinding factor outside the blinding structure. */
    BIGNUM *unblind = NULL;
    BN_BLINDING *blinding = NULL;

    if((ctx = BN_CTX_new()) == NULL) goto err;
    BN_CTX_start(ctx);
    f   = BN_CTX_get(ctx);
    ret = BN_CTX_get(ctx);
    num = BN_num_bytes(rsa->n);
    buf = OPENSSL_malloc(num);
    if(!f || !ret || !buf)
        {
        RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,ERR_R_MALLOC_FAILURE);
        goto err;
        }

    /* This check was for equality but PGP does evil things
     * and chops off the top '0' bytes */
    if (flen > num)
        {
        RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,RSA_R_DATA_GREATER_THAN_MOD_LEN);
        goto err;
        }

    /* make data into a big number */
    if (BN_bin2bn(from,(int)flen,f) == NULL) goto err;

    if (BN_ucmp(f, rsa->n) >= 0)
        {
        RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
        goto err;
        }

    if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
        {
        blinding = rsa_get_blinding(rsa, &local_blinding, ctx);
        if (blinding == NULL)
            {
            RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT, ERR_R_INTERNAL_ERROR);
            goto err;
            }
        }
    
    if (blinding != NULL)
        {
        if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL))
            {
            RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,ERR_R_MALLOC_FAILURE);
            goto err;
            }
        if (!rsa_blinding_convert(blinding, f, unblind, ctx))
            goto err;
        }

    /* do the decrypt */
    if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
        ((rsa->p != NULL) &&
        (rsa->q != NULL) &&
        (rsa->dmp1 != NULL) &&
        (rsa->dmq1 != NULL) &&
        (rsa->iqmp != NULL)) )
        {
        if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx)) goto err;
        }
    else
        {
        BIGNUM local_d;
        BIGNUM *d = NULL;
        
        if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
            {
            d = &local_d;
            BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
            }
        else
            d = rsa->d;

        if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
            if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, CRYPTO_LOCK_RSA, rsa->n, ctx))
                goto err;
        if (!rsa->meth->bn_mod_exp(ret,f,d,rsa->n,ctx,
                rsa->_method_mod_n))
          goto err;
        }

    if (blinding)
        if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
            goto err;

    p=buf;
    j=BN_bn2bin(ret,p); /* j is only used with no-padding mode */

    switch (padding)
        {
    case RSA_PKCS1_PADDING:
        r=RSA_padding_check_PKCS1_type_2(to,num,buf,j,num);
        break;
#ifndef OPENSSL_NO_SHA
        case RSA_PKCS1_OAEP_PADDING:
            r=RSA_padding_check_PKCS1_OAEP(to,num,buf,j,num,NULL,0);
                break;
#endif
    case RSA_SSLV23_PADDING:
        r=RSA_padding_check_SSLv23(to,num,buf,j,num);
        break;
    case RSA_NO_PADDING:
        r=RSA_padding_check_none(to,num,buf,j,num);
        break;
    default:
        RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,RSA_R_UNKNOWN_PADDING_TYPE);
        goto err;
        }
    if (r < 0)
        RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,RSA_R_PADDING_CHECK_FAILED);

err:
    if (ctx != NULL)
        {
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        }
    if (buf != NULL)
        {
        OPENSSL_cleanse(buf,num);
        OPENSSL_free(buf);
        }
    return(r);
    }

/* signature verification */
static int RSA_eay_public_decrypt(int flen, const unsigned char *from,
         unsigned char *to, RSA *rsa, int padding)
    {
    BIGNUM *f,*ret;
    int i,num=0,r= -1;
    unsigned char *p;
    unsigned char *buf=NULL;
    BN_CTX *ctx=NULL;

    if (BN_num_bits(rsa->n) > OPENSSL_RSA_MAX_MODULUS_BITS)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT, RSA_R_MODULUS_TOO_LARGE);
        return -1;
        }

    if (BN_ucmp(rsa->n, rsa->e) <= 0)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT, RSA_R_BAD_E_VALUE);
        return -1;
        }

    /* for large moduli, enforce exponent limit */
    if (BN_num_bits(rsa->n) > OPENSSL_RSA_SMALL_MODULUS_BITS)
        {
        if (BN_num_bits(rsa->e) > OPENSSL_RSA_MAX_PUBEXP_BITS)
            {
            RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT, RSA_R_BAD_E_VALUE);
            return -1;
            }
        }
    
    if((ctx = BN_CTX_new()) == NULL) goto err;
    BN_CTX_start(ctx);
    f = BN_CTX_get(ctx);
    ret = BN_CTX_get(ctx);
    num=BN_num_bytes(rsa->n);
    buf = OPENSSL_malloc(num);
    if(!f || !ret || !buf)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT,ERR_R_MALLOC_FAILURE);
        goto err;
        }

    /* This check was for equality but PGP does evil things
     * and chops off the top '0' bytes */
    if (flen > num)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT,RSA_R_DATA_GREATER_THAN_MOD_LEN);
        goto err;
        }

    if (BN_bin2bn(from,flen,f) == NULL) goto err;

    if (BN_ucmp(f, rsa->n) >= 0)
        {
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT,RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
        goto err;
        }

    if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
        if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, CRYPTO_LOCK_RSA, rsa->n, ctx))
            goto err;

    if (!rsa->meth->bn_mod_exp(ret,f,rsa->e,rsa->n,ctx,
        rsa->_method_mod_n)) goto err;

    if ((padding == RSA_X931_PADDING) && ((ret->d[0] & 0xf) != 12))
        if (!BN_sub(ret, rsa->n, ret)) goto err;

    p=buf;
    i=BN_bn2bin(ret,p);

    switch (padding)
        {
    case RSA_PKCS1_PADDING:
        r=RSA_padding_check_PKCS1_type_1(to,num,buf,i,num);
        break;
    case RSA_X931_PADDING:
        r=RSA_padding_check_X931(to,num,buf,i,num);
        break;
    case RSA_NO_PADDING:
        r=RSA_padding_check_none(to,num,buf,i,num);
        break;
    default:
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT,RSA_R_UNKNOWN_PADDING_TYPE);
        goto err;
        }
    if (r < 0)
        RSAerr(RSA_F_RSA_EAY_PUBLIC_DECRYPT,RSA_R_PADDING_CHECK_FAILED);

err:
    if (ctx != NULL)
        {
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        }
    if (buf != NULL)
        {
        OPENSSL_cleanse(buf,num);
        OPENSSL_free(buf);
        }
    return(r);
    }

static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
    {
    BIGNUM *r1,*m1,*vrfy;
    BIGNUM local_dmp1,local_dmq1,local_c,local_r1;
    BIGNUM *dmp1,*dmq1,*c,*pr1;
    int ret=0;

    BN_CTX_start(ctx);
    r1 = BN_CTX_get(ctx);
    m1 = BN_CTX_get(ctx);
    vrfy = BN_CTX_get(ctx);

    {
        BIGNUM local_p, local_q;
        BIGNUM *p = NULL, *q = NULL;

        /* Make sure BN_mod_inverse in Montgomery intialization uses the
         * BN_FLG_CONSTTIME flag (unless RSA_FLAG_NO_CONSTTIME is set)
         */
        if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
            {
            BN_init(&local_p);
            p = &local_p;
            BN_with_flags(p, rsa->p, BN_FLG_CONSTTIME);

            BN_init(&local_q);
            q = &local_q;
            BN_with_flags(q, rsa->q, BN_FLG_CONSTTIME);
            }
        else
            {
            p = rsa->p;
            q = rsa->q;
            }

        if (rsa->flags & RSA_FLAG_CACHE_PRIVATE)
            {
            if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_p, CRYPTO_LOCK_RSA, p, ctx))
                goto err;
            if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_q, CRYPTO_LOCK_RSA, q, ctx))
                goto err;
            }
    }

    if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
        if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, CRYPTO_LOCK_RSA, rsa->n, ctx))
            goto err;

    /* compute I mod q */
    if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
        {
        c = &local_c;
        BN_with_flags(c, I, BN_FLG_CONSTTIME);
        if (!BN_mod(r1,c,rsa->q,ctx)) goto err;
        }
    else
        {
        if (!BN_mod(r1,I,rsa->q,ctx)) goto err;
        }

    /* compute r1^dmq1 mod q */
    if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
        {
        dmq1 = &local_dmq1;
        BN_with_flags(dmq1, rsa->dmq1, BN_FLG_CONSTTIME);
        }
    else
        dmq1 = rsa->dmq1;
    if (!rsa->meth->bn_mod_exp(m1,r1,dmq1,rsa->q,ctx,
        rsa->_method_mod_q)) goto err;

    /* compute I mod p */
    if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
        {
        c = &local_c;
        BN_with_flags(c, I, BN_FLG_CONSTTIME);
        if (!BN_mod(r1,c,rsa->p,ctx)) goto err;
        }
    else
        {
        if (!BN_mod(r1,I,rsa->p,ctx)) goto err;
        }

    /* compute r1^dmp1 mod p */
    if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
        {
        dmp1 = &local_dmp1;
        BN_with_flags(dmp1, rsa->dmp1, BN_FLG_CONSTTIME);
        }
    else
        dmp1 = rsa->dmp1;
    if (!rsa->meth->bn_mod_exp(r0,r1,dmp1,rsa->p,ctx,
        rsa->_method_mod_p)) goto err;

    if (!BN_sub(r0,r0,m1)) goto err;
    /* This will help stop the size of r0 increasing, which does
     * affect the multiply if it optimised for a power of 2 size */
    if (BN_is_negative(r0))
        if (!BN_add(r0,r0,rsa->p)) goto err;

    if (!BN_mul(r1,r0,rsa->iqmp,ctx)) goto err;

    /* Turn BN_FLG_CONSTTIME flag on before division operation */
    if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
        {
        pr1 = &local_r1;
        BN_with_flags(pr1, r1, BN_FLG_CONSTTIME);
        }
    else
        pr1 = r1;
    if (!BN_mod(r0,pr1,rsa->p,ctx)) goto err;

    /* If p < q it is occasionally possible for the correction of
         * adding 'p' if r0 is negative above to leave the result still
     * negative. This can break the private key operations: the following
     * second correction should *always* correct this rare occurrence.
     * This will *never* happen with OpenSSL generated keys because
         * they ensure p > q [steve]
         */
    if (BN_is_negative(r0))
        if (!BN_add(r0,r0,rsa->p)) goto err;
    if (!BN_mul(r1,r0,rsa->q,ctx)) goto err;
    if (!BN_add(r0,r1,m1)) goto err;

    if (rsa->e && rsa->n)
        {
        if (!rsa->meth->bn_mod_exp(vrfy,r0,rsa->e,rsa->n,ctx,rsa->_method_mod_n)) goto err;
        /* If 'I' was greater than (or equal to) rsa->n, the operation
         * will be equivalent to using 'I mod n'. However, the result of
         * the verify will *always* be less than 'n' so we don't check
         * for absolute equality, just congruency. */
        if (!BN_sub(vrfy, vrfy, I)) goto err;
        if (!BN_mod(vrfy, vrfy, rsa->n, ctx)) goto err;
        if (BN_is_negative(vrfy))
            if (!BN_add(vrfy, vrfy, rsa->n)) goto err;
        if (!BN_is_zero(vrfy))
            {
            /* 'I' and 'vrfy' aren't congruent mod n. Don't leak
             * miscalculated CRT output, just do a raw (slower)
             * mod_exp and return that instead. */

            BIGNUM local_d;
            BIGNUM *d = NULL;
        
            if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME))
                {
                d = &local_d;
                BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
                }
            else
                d = rsa->d;
            if (!rsa->meth->bn_mod_exp(r0,I,d,rsa->n,ctx,
                           rsa->_method_mod_n)) goto err;
            }
        }
    ret=1;
err:
    BN_CTX_end(ctx);
    return(ret);
    }

static int RSA_eay_init(RSA *rsa)
    {
    rsa->flags|=RSA_FLAG_CACHE_PUBLIC|RSA_FLAG_CACHE_PRIVATE;
    return(1);
    }

static int RSA_eay_finish(RSA *rsa)
    {
    if (rsa->_method_mod_n != NULL)
        BN_MONT_CTX_free(rsa->_method_mod_n);
    if (rsa->_method_mod_p != NULL)
        BN_MONT_CTX_free(rsa->_method_mod_p);
    if (rsa->_method_mod_q != NULL)
        BN_MONT_CTX_free(rsa->_method_mod_q);
    return(1);
    }

#endif