317 lines
10 KiB
C
317 lines
10 KiB
C
/* crypto/rsa/rsa_oaep.c */
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/*
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* Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied.
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*/
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/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
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/*
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* See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
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* http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
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* proof for the original OAEP scheme, which EME-OAEP is based on. A new
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* proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
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* "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
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* http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
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* for the underlying permutation: "partial-one-wayness" instead of
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* one-wayness. For the RSA function, this is an equivalent notion.
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*/
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#include "constant_time_locl.h"
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#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
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# include <stdio.h>
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# include "cryptlib.h"
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# include <openssl/bn.h>
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# include <openssl/rsa.h>
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# include <openssl/evp.h>
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# include <openssl/rand.h>
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# include <openssl/sha.h>
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int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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const unsigned char *param, int plen)
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{
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return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
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param, plen, NULL, NULL);
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}
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int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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const unsigned char *param, int plen,
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const EVP_MD *md, const EVP_MD *mgf1md)
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{
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int i, emlen = tlen - 1;
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unsigned char *db, *seed;
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unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
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int mdlen;
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if (md == NULL)
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md = EVP_sha1();
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if (mgf1md == NULL)
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mgf1md = md;
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mdlen = EVP_MD_size(md);
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if (flen > emlen - 2 * mdlen - 1) {
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RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
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RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
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return 0;
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}
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if (emlen < 2 * mdlen + 1) {
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RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
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RSA_R_KEY_SIZE_TOO_SMALL);
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return 0;
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}
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to[0] = 0;
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seed = to + 1;
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db = to + mdlen + 1;
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if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
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return 0;
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memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
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db[emlen - flen - mdlen - 1] = 0x01;
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memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
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if (RAND_bytes(seed, mdlen) <= 0)
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return 0;
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# ifdef PKCS_TESTVECT
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memcpy(seed,
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"\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
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20);
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# endif
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dbmask = OPENSSL_malloc(emlen - mdlen);
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if (dbmask == NULL) {
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RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
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return 0;
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}
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if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
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goto err;
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for (i = 0; i < emlen - mdlen; i++)
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db[i] ^= dbmask[i];
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if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
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goto err;
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for (i = 0; i < mdlen; i++)
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seed[i] ^= seedmask[i];
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OPENSSL_free(dbmask);
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return 1;
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err:
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OPENSSL_free(dbmask);
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return 0;
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}
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int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
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const unsigned char *from, int flen, int num,
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const unsigned char *param, int plen)
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{
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return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
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param, plen, NULL, NULL);
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}
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int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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int num, const unsigned char *param,
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int plen, const EVP_MD *md,
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const EVP_MD *mgf1md)
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{
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int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
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unsigned int good = 0, found_one_byte, mask;
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const unsigned char *maskedseed, *maskeddb;
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/*
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* |em| is the encoded message, zero-padded to exactly |num| bytes: em =
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* Y || maskedSeed || maskedDB
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*/
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unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
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phash[EVP_MAX_MD_SIZE];
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int mdlen;
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if (md == NULL)
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md = EVP_sha1();
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if (mgf1md == NULL)
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mgf1md = md;
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mdlen = EVP_MD_size(md);
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if (tlen <= 0 || flen <= 0)
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return -1;
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/*
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* |num| is the length of the modulus; |flen| is the length of the
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* encoded message. Therefore, for any |from| that was obtained by
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* decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
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* |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
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* the ciphertext, see PKCS #1 v2.2, section 7.1.2.
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* This does not leak any side-channel information.
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*/
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if (num < flen || num < 2 * mdlen + 2) {
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RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
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RSA_R_OAEP_DECODING_ERROR);
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return -1;
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}
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dblen = num - mdlen - 1;
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db = OPENSSL_malloc(dblen);
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if (db == NULL) {
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RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
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goto cleanup;
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}
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em = OPENSSL_malloc(num);
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if (em == NULL) {
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RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
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ERR_R_MALLOC_FAILURE);
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goto cleanup;
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}
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/*
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* Caller is encouraged to pass zero-padded message created with
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* BN_bn2binpad. Trouble is that since we can't read out of |from|'s
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* bounds, it's impossible to have an invariant memory access pattern
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* in case |from| was not zero-padded in advance.
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*/
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for (from += flen, em += num, i = 0; i < num; i++) {
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mask = ~constant_time_is_zero(flen);
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flen -= 1 & mask;
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from -= 1 & mask;
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*--em = *from & mask;
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}
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/*
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* The first byte must be zero, however we must not leak if this is
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* true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
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* Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
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*/
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good = constant_time_is_zero(em[0]);
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maskedseed = em + 1;
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maskeddb = em + 1 + mdlen;
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if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
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goto cleanup;
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for (i = 0; i < mdlen; i++)
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seed[i] ^= maskedseed[i];
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if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
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goto cleanup;
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for (i = 0; i < dblen; i++)
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db[i] ^= maskeddb[i];
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if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
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goto cleanup;
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good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
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found_one_byte = 0;
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for (i = mdlen; i < dblen; i++) {
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/*
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* Padding consists of a number of 0-bytes, followed by a 1.
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*/
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unsigned int equals1 = constant_time_eq(db[i], 1);
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unsigned int equals0 = constant_time_is_zero(db[i]);
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one_index = constant_time_select_int(~found_one_byte & equals1,
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i, one_index);
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found_one_byte |= equals1;
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good &= (found_one_byte | equals0);
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}
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good &= found_one_byte;
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/*
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* At this point |good| is zero unless the plaintext was valid,
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* so plaintext-awareness ensures timing side-channels are no longer a
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* concern.
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*/
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msg_index = one_index + 1;
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mlen = dblen - msg_index;
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/*
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* For good measure, do this check in constant time as well.
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*/
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good &= constant_time_ge(tlen, mlen);
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/*
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* Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
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* Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
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* Otherwise leave |to| unchanged.
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* Copy the memory back in a way that does not reveal the size of
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* the data being copied via a timing side channel. This requires copying
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* parts of the buffer multiple times based on the bits set in the real
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* length. Clear bits do a non-copy with identical access pattern.
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* The loop below has overall complexity of O(N*log(N)).
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*/
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tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
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dblen - mdlen - 1, tlen);
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for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
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mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
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for (i = mdlen + 1; i < dblen - msg_index; i++)
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db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
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}
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for (i = 0; i < tlen; i++) {
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mask = good & constant_time_lt(i, mlen);
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to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
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}
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/*
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* To avoid chosen ciphertext attacks, the error message should not
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* reveal which kind of decoding error happened.
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*/
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RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
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RSA_R_OAEP_DECODING_ERROR);
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err_clear_last_constant_time(1 & good);
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cleanup:
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OPENSSL_cleanse(seed, sizeof(seed));
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OPENSSL_cleanse(db, dblen);
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OPENSSL_free(db);
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OPENSSL_cleanse(em, num);
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OPENSSL_free(em);
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return constant_time_select_int(good, mlen, -1);
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}
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int PKCS1_MGF1(unsigned char *mask, long len,
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const unsigned char *seed, long seedlen, const EVP_MD *dgst)
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{
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long i, outlen = 0;
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unsigned char cnt[4];
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EVP_MD_CTX c;
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unsigned char md[EVP_MAX_MD_SIZE];
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int mdlen;
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int rv = -1;
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EVP_MD_CTX_init(&c);
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mdlen = EVP_MD_size(dgst);
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if (mdlen < 0)
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goto err;
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for (i = 0; outlen < len; i++) {
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cnt[0] = (unsigned char)((i >> 24) & 255);
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cnt[1] = (unsigned char)((i >> 16) & 255);
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cnt[2] = (unsigned char)((i >> 8)) & 255;
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cnt[3] = (unsigned char)(i & 255);
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if (!EVP_DigestInit_ex(&c, dgst, NULL)
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|| !EVP_DigestUpdate(&c, seed, seedlen)
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|| !EVP_DigestUpdate(&c, cnt, 4))
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goto err;
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if (outlen + mdlen <= len) {
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if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
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goto err;
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outlen += mdlen;
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} else {
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if (!EVP_DigestFinal_ex(&c, md, NULL))
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goto err;
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memcpy(mask + outlen, md, len - outlen);
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outlen = len;
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}
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}
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rv = 0;
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err:
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EVP_MD_CTX_cleanup(&c);
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return rv;
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}
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#endif
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