/*

 * Copyright 1999-2024 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */

/*

 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:

 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security

 * proof for the original OAEP scheme, which EME-OAEP is based on. A new

 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,

 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:

 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements

 * for the underlying permutation: "partial-one-wayness" instead of

 * one-wayness.  For the RSA function, this is an equivalent notion.

 */

/*

 * RSA low level APIs are deprecated for public use, but still ok for

 * internal use.

 */

#include "internal/deprecated.h"

#include "internal/constant_time.h"

#include <stdio.h>

#include "internal/cryptlib.h"

#include <openssl/bn.h>

#include <openssl/evp.h>

#include <openssl/rand.h>

#include <openssl/sha.h>

#include "rsa_local.h"

int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,

                               const unsigned char *from, int flen,

                               const unsigned char *param, int plen)

{

    return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,

                                                   param, plen, NULL, NULL);

}

/*

 * Perform the padding as per NIST 800-56B 7.2.2.3

 *      from (K) is the key material.

 *      param (A) is the additional input.

 * Step numbers are included here but not in the constant time inverse below

 * to avoid complicating an already difficult enough function.

 */

int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx,

                                            unsigned char *to, int tlen,

                                            const unsigned char *from, int flen,

                                            const unsigned char *param,

                                            int plen, const EVP_MD *md,

                                            const EVP_MD *mgf1md)

{

    int rv = 0;

    int i, emlen = tlen - 1;

    unsigned char *db, *seed;

    unsigned char *dbmask = NULL;

    unsigned char seedmask[EVP_MAX_MD_SIZE];

    int mdlen, dbmask_len = 0;

    if (md == NULL) {

#ifndef FIPS_MODULE

        md = EVP_sha1();

#else

        ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);

        return 0;

#endif

    }

    if (mgf1md == NULL)

        mgf1md = md;

#ifdef FIPS_MODULE

    /* XOF are approved as standalone; Shake256 in Ed448; MGF */

    if (EVP_MD_xof(md)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);

        return 0;

    }

    if (EVP_MD_xof(mgf1md)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);

        return 0;

    }

#endif

    mdlen = EVP_MD_get_size(md);

    if (mdlen <= 0) {

        ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);

        return 0;

    }

    /* step 2b: check KLen > nLen - 2 HLen - 2 */

    if (flen > emlen - 2 * mdlen - 1) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);

        return 0;

    }

    if (emlen < 2 * mdlen + 1) {

        ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);

        return 0;

    }

    /* step 3i: EM = 00000000 || maskedMGF || maskedDB */

    to[0] = 0;

    seed = to + 1;

    db = to + mdlen + 1;

    /* step 3a: hash the additional input */

    if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))

        goto err;

    /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */

    memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);

    /* step 3c: DB = HA || PS || 00000001 || K */

    db[emlen - flen - mdlen - 1] = 0x01;

    memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);

    /* step 3d: generate random byte string */

    if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0)

        goto err;

    dbmask_len = emlen - mdlen;

    dbmask = OPENSSL_malloc(dbmask_len);

    if (dbmask == NULL)

        goto err;

    /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */

    if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)

        goto err;

    /* step 3f: maskedDB = DB XOR dbMask */

    for (i = 0; i < dbmask_len; i++)

        db[i] ^= dbmask[i];

    /* step 3g: mgfSeed = MGF(maskedDB, HLen) */

    if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)

        goto err;

    /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */

    for (i = 0; i < mdlen; i++)

        seed[i] ^= seedmask[i];

    rv = 1;

 err:

    OPENSSL_cleanse(seedmask, sizeof(seedmask));

    OPENSSL_clear_free(dbmask, dbmask_len);

    return rv;

}

int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,

                                    const unsigned char *from, int flen,

                                    const unsigned char *param, int plen,

                                    const EVP_MD *md, const EVP_MD *mgf1md)

{

    return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,

                                                   param, plen, md, mgf1md);

}

int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,

                                 const unsigned char *from, int flen, int num,

                                 const unsigned char *param, int plen)

{

    return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,

                                             param, plen, NULL, NULL);

}

int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,

                                      const unsigned char *from, int flen,

                                      int num, const unsigned char *param,

                                      int plen, const EVP_MD *md,

                                      const EVP_MD *mgf1md)

{

    int i, dblen = 0, mlen = -1, one_index = 0, msg_index;

    unsigned int good = 0, found_one_byte, mask;

    const unsigned char *maskedseed, *maskeddb;

    /*

     * |em| is the encoded message, zero-padded to exactly |num| bytes: em =

     * Y || maskedSeed || maskedDB

     */

    unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],

        phash[EVP_MAX_MD_SIZE];

    int mdlen;

    if (md == NULL) {

#ifndef FIPS_MODULE

        md = EVP_sha1();

#else

        ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);

        return -1;

#endif

    }

    if (mgf1md == NULL)

        mgf1md = md;

#ifdef FIPS_MODULE

    /* XOF are approved as standalone; Shake256 in Ed448; MGF */

    if (EVP_MD_xof(md)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);

        return -1;

    }

    if (EVP_MD_xof(mgf1md)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);

        return -1;

    }

#endif

    mdlen = EVP_MD_get_size(md);

    if (tlen <= 0 || flen <= 0 || mdlen <= 0)

        return -1;

    /*

     * |num| is the length of the modulus; |flen| is the length of the

     * encoded message. Therefore, for any |from| that was obtained by

     * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,

     * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of

     * the ciphertext, see PKCS #1 v2.2, section 7.1.2.

     * This does not leak any side-channel information.

     */

    if (num < flen || num < 2 * mdlen + 2) {

        ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);

        return -1;

    }

    dblen = num - mdlen - 1;

    db = OPENSSL_malloc(dblen);

    if (db == NULL)

        goto cleanup;

    em = OPENSSL_malloc(num);

    if (em == NULL)

        goto cleanup;

    /*

     * Caller is encouraged to pass zero-padded message created with

     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s

     * bounds, it's impossible to have an invariant memory access pattern

     * in case |from| was not zero-padded in advance.

     */

    for (from += flen, em += num, i = 0; i < num; i++) {

        mask = ~constant_time_is_zero(flen);

        flen -= 1 & mask;

        from -= 1 & mask;

        *--em = *from & mask;

    }

    /*

     * The first byte must be zero, however we must not leak if this is

     * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA

     * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).

     */

    good = constant_time_is_zero(em[0]);

    maskedseed = em + 1;

    maskeddb = em + 1 + mdlen;

    if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))

        goto cleanup;

    for (i = 0; i < mdlen; i++)

        seed[i] ^= maskedseed[i];

    if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))

        goto cleanup;

    for (i = 0; i < dblen; i++)

        db[i] ^= maskeddb[i];

    if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))

        goto cleanup;

    good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));

    found_one_byte = 0;

    for (i = mdlen; i < dblen; i++) {

        /*

         * Padding consists of a number of 0-bytes, followed by a 1.

         */

        unsigned int equals1 = constant_time_eq(db[i], 1);

        unsigned int equals0 = constant_time_is_zero(db[i]);

        one_index = constant_time_select_int(~found_one_byte & equals1,

                                             i, one_index);

        found_one_byte |= equals1;

        good &= (found_one_byte | equals0);

    }

    good &= found_one_byte;

    /*

     * At this point |good| is zero unless the plaintext was valid,

     * so plaintext-awareness ensures timing side-channels are no longer a

     * concern.

     */

    msg_index = one_index + 1;

    mlen = dblen - msg_index;

    /*

     * For good measure, do this check in constant time as well.

     */

    good &= constant_time_ge(tlen, mlen);

    /*

     * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.

     * Otherwise leave |to| unchanged.

     * Copy the memory back in a way that does not reveal the size of

     * the data being copied via a timing side channel. This requires copying

     * parts of the buffer multiple times based on the bits set in the real

     * length. Clear bits do a non-copy with identical access pattern.

     * The loop below has overall complexity of O(N*log(N)).

     */

    tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),

                                    dblen - mdlen - 1, tlen);

    for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);

        for (i = mdlen + 1; i < dblen - msg_index; i++)

            db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);

    }

    for (i = 0; i < tlen; i++) {

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);

    }

#ifndef FIPS_MODULE

    /*

     * To avoid chosen ciphertext attacks, the error message should not

     * reveal which kind of decoding error happened.

     *

     * This trick doesn't work in the FIPS provider because libcrypto manages

     * the error stack. Instead we opt not to put an error on the stack at all

     * in case of padding failure in the FIPS provider.

     */

    ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);

    err_clear_last_constant_time(1 & good);

#endif

 cleanup:

    OPENSSL_cleanse(seed, sizeof(seed));

    OPENSSL_clear_free(db, dblen);

    OPENSSL_clear_free(em, num);

    return constant_time_select_int(good, mlen, -1);

}

/*

 * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.

 * The variables are named differently to NIST:

 *      mask (T) and len (maskLen)are the returned mask.

 *      seed (mgfSeed).

 * The range checking steps inm the process are performed outside.

 */

int PKCS1_MGF1(unsigned char *mask, long len,

               const unsigned char *seed, long seedlen, const EVP_MD *dgst)

{

    long i, outlen = 0;

    unsigned char cnt[4];

    EVP_MD_CTX *c = EVP_MD_CTX_new();

    unsigned char md[EVP_MAX_MD_SIZE];

    int mdlen;

    int rv = -1;

    if (c == NULL)

        goto err;

    mdlen = EVP_MD_get_size(dgst);

    if (mdlen <= 0)

        goto err;

    /* step 4 */

    for (i = 0; outlen < len; i++) {

        /* step 4a: D = I2BS(counter, 4) */

        cnt[0] = (unsigned char)((i >> 24) & 255);

        cnt[1] = (unsigned char)((i >> 16) & 255);

        cnt[2] = (unsigned char)((i >> 8)) & 255;

        cnt[3] = (unsigned char)(i & 255);

        /* step 4b: T =T || hash(mgfSeed || D) */

        if (!EVP_DigestInit_ex(c, dgst, NULL)

            || !EVP_DigestUpdate(c, seed, seedlen)

            || !EVP_DigestUpdate(c, cnt, 4))

            goto err;

        if (outlen + mdlen <= len) {

            if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))

                goto err;

            outlen += mdlen;

        } else {

            if (!EVP_DigestFinal_ex(c, md, NULL))

                goto err;

            memcpy(mask + outlen, md, len - outlen);

            outlen = len;

        }

    }

    rv = 0;

 err:

    OPENSSL_cleanse(md, sizeof(md));

    EVP_MD_CTX_free(c);

    return rv;

}