/*

 * Copyright 1995-2023 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

 */

/*

 * 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 <openssl/bn.h>

#include <openssl/rsa.h>

#include <openssl/rand.h>

/* Just for the SSL_MAX_MASTER_KEY_LENGTH value */

#include <openssl/prov_ssl.h>

#include <openssl/evp.h>

#include <openssl/sha.h>

#include <openssl/hmac.h>

#include "internal/cryptlib.h"

#include "crypto/rsa.h"

#include "rsa_local.h"

int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,

    const unsigned char *from, int flen)

{

    int j;

    unsigned char *p;

    if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);

        return 0;

    }

    p = (unsigned char *)to;

    *(p++) = 0;

    *(p++) = 1; /* Private Key BT (Block Type) */

    /* pad out with 0xff data */

    j = tlen - 3 - flen;

    memset(p, 0xff, j);

    p += j;

    *(p++) = '\0';

    memcpy(p, from, (unsigned int)flen);

    return 1;

}

int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,

    const unsigned char *from, int flen,

    int num)

{

    int i, j;

    const unsigned char *p;

    p = from;

    /*

     * The format is

     * 00 || 01 || PS || 00 || D

     * PS - padding string, at least 8 bytes of FF

     * D  - data.

     */

    if (num < RSA_PKCS1_PADDING_SIZE)

        return -1;

    /* Accept inputs with and without the leading 0-byte. */

    if (num == flen) {

        if ((*p++) != 0x00) {

            ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_PADDING);

            return -1;

        }

        flen--;

    }

    if ((num != (flen + 1)) || (*(p++) != 0x01)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_BLOCK_TYPE_IS_NOT_01);

        return -1;

    }

    /* scan over padding data */

    j = flen - 1; /* one for type. */

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

        if (*p != 0xff) { /* should decrypt to 0xff */

            if (*p == 0) {

                p++;

                break;

            } else {

                ERR_raise(ERR_LIB_RSA, RSA_R_BAD_FIXED_HEADER_DECRYPT);

                return -1;

            }

        }

        p++;

    }

    if (i == j) {

        ERR_raise(ERR_LIB_RSA, RSA_R_NULL_BEFORE_BLOCK_MISSING);

        return -1;

    }

    if (i < 8) {

        ERR_raise(ERR_LIB_RSA, RSA_R_BAD_PAD_BYTE_COUNT);

        return -1;

    }

    i++; /* Skip over the '\0' */

    j -= i;

    if (j > tlen) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE);

        return -1;

    }

    memcpy(to, p, (unsigned int)j);

    return j;

}

int ossl_rsa_padding_add_PKCS1_type_2_ex(OSSL_LIB_CTX *libctx, unsigned char *to,

    int tlen, const unsigned char *from,

    int flen)

{

    int i, j;

    unsigned char *p;

    if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {

        ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);

        return 0;

    } else if (flen < 0) {

        ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);

        return 0;

    }

    p = (unsigned char *)to;

    *(p++) = 0;

    *(p++) = 2; /* Public Key BT (Block Type) */

    /* pad out with non-zero random data */

    j = tlen - 3 - flen;

    if (RAND_bytes_ex(libctx, p, j, 0) <= 0)

        return 0;

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

        if (*p == '\0')

            do {

                if (RAND_bytes_ex(libctx, p, 1, 0) <= 0)

                    return 0;

            } while (*p == '\0');

        p++;

    }

    *(p++) = '\0';

    memcpy(p, from, (unsigned int)flen);

    return 1;

}

int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,

    const unsigned char *from, int flen)

{

    return ossl_rsa_padding_add_PKCS1_type_2_ex(NULL, to, tlen, from, flen);

}

int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,

    const unsigned char *from, int flen,

    int num)

{

    int i;

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

    unsigned char *em = NULL;

    unsigned int good, found_zero_byte, mask;

    int zero_index = 0, msg_index, mlen = -1;

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

        return -1;

    /*

     * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",

     * section 7.2.2.

     */

    if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {

        ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);

        return -1;

    }

    em = OPENSSL_malloc(num);

    if (em == NULL)

        return -1;

    /*

     * 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;

    }

    good = constant_time_is_zero(em[0]);

    good &= constant_time_eq(em[1], 2);

    /* scan over padding data */

    found_zero_byte = 0;

    for (i = 2; i < num; i++) {

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

        zero_index = constant_time_select_int(~found_zero_byte & equals0,

            i, zero_index);

        found_zero_byte |= equals0;

    }

    /*

     * PS must be at least 8 bytes long, and it starts two bytes into |em|.

     * If we never found a 0-byte, then |zero_index| is 0 and the check

     * also fails.

     */

    good &= constant_time_ge(zero_index, 2 + 8);

    /*

     * Skip the zero byte. This is incorrect if we never found a zero-byte

     * but in this case we also do not copy the message out.

     */

    msg_index = zero_index + 1;

    mlen = num - 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 |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE 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(num - RSA_PKCS1_PADDING_SIZE, tlen),

        num - RSA_PKCS1_PADDING_SIZE, tlen);

    for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);

        for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)

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

    }

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

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);

    }

    OPENSSL_clear_free(em, num);

#ifndef FIPS_MODULE

    /*

     * 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_PKCS_DECODING_ERROR);

    err_clear_last_constant_time(1 & good);

#endif

    return constant_time_select_int(good, mlen, -1);

}

static int ossl_rsa_prf(OSSL_LIB_CTX *ctx,

    unsigned char *to, int tlen,

    const char *label, int llen,

    const unsigned char *kdk,

    uint16_t bitlen)

{

    int pos;

    int ret = -1;

    uint16_t iter = 0;

    unsigned char be_iter[sizeof(iter)];

    unsigned char be_bitlen[sizeof(bitlen)];

    HMAC_CTX *hmac = NULL;

    EVP_MD *md = NULL;

    unsigned char hmac_out[SHA256_DIGEST_LENGTH];

    unsigned int md_len;

    if (tlen * 8 != bitlen) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        return ret;

    }

    be_bitlen[0] = (bitlen >> 8) & 0xff;

    be_bitlen[1] = bitlen & 0xff;

    hmac = HMAC_CTX_new();

    if (hmac == NULL) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        goto err;

    }

    /*

     * we use hardcoded hash so that migrating between versions that use

     * different hash doesn't provide a Bleichenbacher oracle:

     * if the attacker can see that different versions return different

     * messages for the same ciphertext, they'll know that the message is

     * synthetically generated, which means that the padding check failed

     */

    md = EVP_MD_fetch(ctx, "sha256", NULL);

    if (md == NULL) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        goto err;

    }

    if (HMAC_Init_ex(hmac, kdk, SHA256_DIGEST_LENGTH, md, NULL) <= 0) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        goto err;

    }

    for (pos = 0; pos < tlen; pos += SHA256_DIGEST_LENGTH, iter++) {

        if (HMAC_Init_ex(hmac, NULL, 0, NULL, NULL) <= 0) {

            ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

            goto err;

        }

        be_iter[0] = (iter >> 8) & 0xff;

        be_iter[1] = iter & 0xff;

        if (HMAC_Update(hmac, be_iter, sizeof(be_iter)) <= 0) {

            ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

            goto err;

        }

        if (HMAC_Update(hmac, (unsigned char *)label, llen) <= 0) {

            ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

            goto err;

        }

        if (HMAC_Update(hmac, be_bitlen, sizeof(be_bitlen)) <= 0) {

            ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

            goto err;

        }

        /*

         * HMAC_Final requires the output buffer to fit the whole MAC

         * value, so we need to use the intermediate buffer for the last

         * unaligned block

         */

        md_len = SHA256_DIGEST_LENGTH;

        if (pos + SHA256_DIGEST_LENGTH > tlen) {

            if (HMAC_Final(hmac, hmac_out, &md_len) <= 0) {

                ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

                goto err;

            }

            memcpy(to + pos, hmac_out, tlen - pos);

        } else {

            if (HMAC_Final(hmac, to + pos, &md_len) <= 0) {

                ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

                goto err;

            }

        }

    }

    ret = 0;

err:

    HMAC_CTX_free(hmac);

    EVP_MD_free(md);

    return ret;

}

/*

 * ossl_rsa_padding_check_PKCS1_type_2() checks and removes the PKCS#1 type 2

 * padding from a decrypted RSA message. Unlike the

 * RSA_padding_check_PKCS1_type_2() it will not return an error in case it

 * detects a padding error, rather it will return a deterministically generated

 * random message. In other words it will perform an implicit rejection

 * of an invalid padding. This means that the returned value does not indicate

 * if the padding of the encrypted message was correct or not, making

 * side channel attacks like the ones described by Bleichenbacher impossible

 * without access to the full decrypted value and a brute-force search of

 * remaining padding bytes

 */

int ossl_rsa_padding_check_PKCS1_type_2(OSSL_LIB_CTX *ctx,

    unsigned char *to, int tlen,

    const unsigned char *from, int flen,

    int num, unsigned char *kdk)

{

/*

 * We need to generate a random length for the synthetic message, to avoid

 * bias towards zero and avoid non-constant timeness of DIV, we prepare

 * 128 values to check if they are not too large for the used key size,

 * and use 0 in case none of them are small enough, as 2^-128 is a good enough

 * safety margin

 */

#define MAX_LEN_GEN_TRIES 128

    unsigned char *synthetic = NULL;

    int synthetic_length;

    uint16_t len_candidate;

    unsigned char candidate_lengths[MAX_LEN_GEN_TRIES * sizeof(len_candidate)];

    uint16_t len_mask;

    uint16_t max_sep_offset;

    int synth_msg_index = 0;

    int ret = -1;

    int i, j;

    unsigned int good, found_zero_byte;

    int zero_index = 0, msg_index;

    /*

     * If these checks fail then either the message in publicly invalid, or

     * we've been called incorrectly. We can fail immediately.

     * Since this code is called only internally by openssl, those are just

     * sanity checks

     */

    if (num != flen || tlen <= 0 || flen <= 0) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        return -1;

    }

    /* Generate a random message to return in case the padding checks fail */

    synthetic = OPENSSL_malloc(flen);

    if (synthetic == NULL) {

        ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);

        return -1;

    }

    if (ossl_rsa_prf(ctx, synthetic, flen, "message", 7, kdk, flen * 8) < 0)

        goto err;

    /* decide how long the random message should be */

    if (ossl_rsa_prf(ctx, candidate_lengths, sizeof(candidate_lengths),

            "length", 6, kdk,

            MAX_LEN_GEN_TRIES * sizeof(len_candidate) * 8)

        < 0)

        goto err;

    /*

     * max message size is the size of the modulus size less 2 bytes for

     * version and padding type and a minimum of 8 bytes padding

     */

    len_mask = max_sep_offset = flen - 2 - 8;

    /*

     * we want a mask so lets propagate the high bit to all positions less

     * significant than it

     */

    len_mask |= len_mask >> 1;

    len_mask |= len_mask >> 2;

    len_mask |= len_mask >> 4;

    len_mask |= len_mask >> 8;

    synthetic_length = 0;

    for (i = 0; i < MAX_LEN_GEN_TRIES * (int)sizeof(len_candidate);

        i += sizeof(len_candidate)) {

        len_candidate = (candidate_lengths[i] << 8) | candidate_lengths[i + 1];

        len_candidate &= len_mask;

        synthetic_length = constant_time_select_int(

            constant_time_lt(len_candidate, max_sep_offset),

            len_candidate, synthetic_length);

    }

    synth_msg_index = flen - synthetic_length;

    /* we have alternative message ready, check the real one */

    good = constant_time_is_zero(from[0]);

    good &= constant_time_eq(from[1], 2);

    /* then look for the padding|message separator (the first zero byte) */

    found_zero_byte = 0;

    for (i = 2; i < flen; i++) {

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

        zero_index = constant_time_select_int(~found_zero_byte & equals0,

            i, zero_index);

        found_zero_byte |= equals0;

    }

    /*

     * padding must be at least 8 bytes long, and it starts two bytes into

     * |from|. If we never found a 0-byte, then |zero_index| is 0 and the check

     * also fails.

     */

    good &= constant_time_ge(zero_index, 2 + 8);

    /*

     * Skip the zero byte. This is incorrect if we never found a zero-byte

     * but in this case we also do not copy the message out.

     */

    msg_index = zero_index + 1;

    /*

     * old code returned an error in case the decrypted message wouldn't fit

     * into the |to|, since that would leak information, return the synthetic

     * message instead

     */

    good &= constant_time_ge(tlen, num - msg_index);

    msg_index = constant_time_select_int(good, msg_index, synth_msg_index);

    /*

     * since at this point the |msg_index| does not provide the signal

     * indicating if the padding check failed or not, we don't have to worry

     * about leaking the length of returned message, we still need to ensure

     * that we read contents of both buffers so that cache accesses don't leak

     * the value of |good|

     */

    for (i = msg_index, j = 0; i < flen && j < tlen; i++, j++)

        to[j] = constant_time_select_8(good, from[i], synthetic[i]);

    ret = j;

err:

    /*

     * the only time ret < 0 is when the ciphertext is publicly invalid

     * or we were called with invalid parameters, so we don't have to perform

     * a side-channel secure raising of the error

     */

    if (ret < 0)

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

    OPENSSL_free(synthetic);

    return ret;

}

/*

 * ossl_rsa_padding_check_PKCS1_type_2_TLS() checks and removes the PKCS1 type 2

 * padding from a decrypted RSA message in a TLS signature. The result is stored

 * in the buffer pointed to by |to| which should be |tlen| bytes long. |tlen|

 * must be at least SSL_MAX_MASTER_KEY_LENGTH. The original decrypted message

 * should be stored in |from| which must be |flen| bytes in length and padded

 * such that |flen == RSA_size()|. The TLS protocol version that the client

 * originally requested should be passed in |client_version|. Some buggy clients

 * can exist which use the negotiated version instead of the originally

 * requested protocol version. If it is necessary to work around this bug then

 * the negotiated protocol version can be passed in |alt_version|, otherwise 0

 * should be passed.

 *

 * If the passed message is publicly invalid or some other error that can be

 * treated in non-constant time occurs then -1 is returned. On success the

 * length of the decrypted data is returned. This will always be

 * SSL_MAX_MASTER_KEY_LENGTH. If an error occurs that should be treated in

 * constant time then this function will appear to return successfully, but the

 * decrypted data will be randomly generated (as per

 * https://tools.ietf.org/html/rfc5246#section-7.4.7.1).

 */

int ossl_rsa_padding_check_PKCS1_type_2_TLS(OSSL_LIB_CTX *libctx,

    unsigned char *to, size_t tlen,

    const unsigned char *from,

    size_t flen, int client_version,

    int alt_version)

{

    unsigned int i, good, version_good;

    unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];

    /*

     * If these checks fail then either the message in publicly invalid, or

     * we've been called incorrectly. We can fail immediately.

     */

    if (flen < RSA_PKCS1_PADDING_SIZE + SSL_MAX_MASTER_KEY_LENGTH

        || tlen < SSL_MAX_MASTER_KEY_LENGTH) {

        ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);

        return -1;

    }

    /*

     * Generate a random premaster secret to use in the event that we fail

     * to decrypt.

     */

    if (RAND_priv_bytes_ex(libctx, rand_premaster_secret,

            sizeof(rand_premaster_secret), 0)

        <= 0) {

        ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);

        return -1;

    }

    good = constant_time_is_zero(from[0]);

    good &= constant_time_eq(from[1], 2);

    /* Check we have the expected padding data */

    for (i = 2; i < flen - SSL_MAX_MASTER_KEY_LENGTH - 1; i++)

        good &= ~constant_time_is_zero_8(from[i]);

    good &= constant_time_is_zero_8(from[flen - SSL_MAX_MASTER_KEY_LENGTH - 1]);

    /*

     * If the version in the decrypted pre-master secret is correct then

     * version_good will be 0xff, otherwise it'll be zero. The

     * Klima-Pokorny-Rosa extension of Bleichenbacher's attack

     * (http://eprint.iacr.org/2003/052/) exploits the version number

     * check as a "bad version oracle". Thus version checks are done in

     * constant time and are treated like any other decryption error.

     */

    version_good = constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],

        (client_version >> 8) & 0xff);

    version_good &= constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],

        client_version & 0xff);

    /*

     * The premaster secret must contain the same version number as the

     * ClientHello to detect version rollback attacks (strangely, the

     * protocol does not offer such protection for DH ciphersuites).

     * However, buggy clients exist that send the negotiated protocol

     * version instead if the server does not support the requested

     * protocol version. If SSL_OP_TLS_ROLLBACK_BUG is set then we tolerate

     * such clients. In that case alt_version will be non-zero and set to

     * the negotiated version.

     */

    if (alt_version > 0) {

        unsigned int workaround_good;

        workaround_good = constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],

            (alt_version >> 8) & 0xff);

        workaround_good &= constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],

            alt_version & 0xff);

        version_good |= workaround_good;

    }

    good &= version_good;

    /*

     * Now copy the result over to the to buffer if good, or random data if

     * not good.

     */

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

        to[i] = constant_time_select_8(good,

            from[flen - SSL_MAX_MASTER_KEY_LENGTH + i],

            rand_premaster_secret[i]);

    }

    /*

     * We must not leak whether a decryption failure occurs because of

     * Bleichenbacher's attack on PKCS #1 v1.5 RSA padding (see RFC 2246,

     * section 7.4.7.1). The code follows that advice of the TLS RFC and

     * generates a random premaster secret for the case that the decrypt

     * fails. See https://tools.ietf.org/html/rfc5246#section-7.4.7.1

     * So, whether we actually succeeded or not, return success.

     */

    return SSL_MAX_MASTER_KEY_LENGTH;

}