rsa_oaep.c

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/* crypto/rsa/rsa_oaep.c */
/* Written by Ulf Moeller. This software is distributed on an "AS IS"
   basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. */

/* 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.
 */


#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/sha.h>

static int MGF1(unsigned char *mask, long len,
    const unsigned char *seed, long seedlen);

int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
    const unsigned char *from, int flen,
    const unsigned char *param, int plen)
    {
    int i, emlen = tlen - 1;
    unsigned char *db, *seed;
    unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];

    if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1)
        {
        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
           RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
        return 0;
        }

    if (emlen < 2 * SHA_DIGEST_LENGTH + 1)
        {
        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
        return 0;
        }

    to[0] = 0;
    seed = to + 1;
    db = to + SHA_DIGEST_LENGTH + 1;

    if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
        return 0;
    memset(db + SHA_DIGEST_LENGTH, 0,
        emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
    db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
    memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen);
    if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
        return 0;
#ifdef PKCS_TESTVECT
    memcpy(seed,
       "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
       20);
#endif

    dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
    if (dbmask == NULL)
        {
        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
        return 0;
        }

    if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0)
        return 0;
    for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
        db[i] ^= dbmask[i];

    if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0)
        return 0;
    for (i = 0; i < SHA_DIGEST_LENGTH; i++)
        seed[i] ^= seedmask[i];

    OPENSSL_free(dbmask);
    return 1;
    }

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)
    {
    int i, dblen, mlen = -1;
    const unsigned char *maskeddb;
    int lzero;
    unsigned char *db = NULL, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
    unsigned char *padded_from;
    int bad = 0;

    if (--num < 2 * SHA_DIGEST_LENGTH + 1)
        /* 'num' is the length of the modulus, i.e. does not depend on the
         * particular ciphertext. */
        goto decoding_err;

    lzero = num - flen;
    if (lzero < 0)
        {
        /* signalling this error immediately after detection might allow
         * for side-channel attacks (e.g. timing if 'plen' is huge
         * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA Optimal
         * Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001),
         * so we use a 'bad' flag */
        bad = 1;
        lzero = 0;
        flen = num; /* don't overflow the memcpy to padded_from */
        }

    dblen = num - SHA_DIGEST_LENGTH;
    db = OPENSSL_malloc(dblen + num);
    if (db == NULL)
        {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
        return -1;
        }

    /* Always do this zero-padding copy (even when lzero == 0)
     * to avoid leaking timing info about the value of lzero. */
    padded_from = db + dblen;
    memset(padded_from, 0, lzero);
    memcpy(padded_from + lzero, from, flen);

    maskeddb = padded_from + SHA_DIGEST_LENGTH;

    if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
        return -1;
    for (i = 0; i < SHA_DIGEST_LENGTH; i++)
        seed[i] ^= padded_from[i];
  
    if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
        return -1;
    for (i = 0; i < dblen; i++)
        db[i] ^= maskeddb[i];

    if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
        return -1;

    if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
        goto decoding_err;
    else
        {
        for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
            if (db[i] != 0x00)
                break;
        if (i == dblen || db[i] != 0x01)
            goto decoding_err;
        else
            {
            /* everything looks OK */

            mlen = dblen - ++i;
            if (tlen < mlen)
                {
                RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
                mlen = -1;
                }
            else
                memcpy(to, db + i, mlen);
            }
        }
    OPENSSL_free(db);
    return mlen;

decoding_err:
    /* to avoid chosen ciphertext attacks, the error message should not reveal
     * which kind of decoding error happened */
    RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
    if (db != NULL) OPENSSL_free(db);
    return -1;
    }

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;
    unsigned char md[EVP_MAX_MD_SIZE];
    int mdlen;
    int rv = -1;

    EVP_MD_CTX_init(&c);
    mdlen = EVP_MD_size(dgst);
    if (mdlen < 0)
        goto err;
    for (i = 0; outlen < len; i++)
        {
        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);
        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:
    EVP_MD_CTX_cleanup(&c);
    return rv;
    }

static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
         long seedlen)
    {
    return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
    }
#endif