Commit a766aab9 authored by Billy Brumley's avatar Billy Brumley Committed by Richard Levitte
Browse files

[crypto/ec] don't assume points are of order group->order 



Reviewed-by: default avatarPaul Dale <paul.dale@oracle.com>
Reviewed-by: default avatarRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6535)
parent 27232cc3

crypto/ec/ec_mult.c

+15 −14
Original line number Diff line number Diff line
@@ -132,10 +132,11 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, 
                            const BIGNUM *scalar, const EC_POINT *point,

                            BN_CTX *ctx)

{

    int i, order_bits, group_top, kbit, pbit, Z_is_one;

    int i, cardinality_bits, group_top, kbit, pbit, Z_is_one;

    EC_POINT *s = NULL;

    BIGNUM *k = NULL;

    BIGNUM *lambda = NULL;

    BIGNUM *cardinality = NULL;

    BN_CTX *new_ctx = NULL;

    int ret = 0;
@@ -144,8 +145,6 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, 


    BN_CTX_start(ctx);



    order_bits = BN_num_bits(group->order);



    s = EC_POINT_new(group);

    if (s == NULL)

        goto err;
@@ -160,18 +159,20 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, 


    EC_POINT_BN_set_flags(s, BN_FLG_CONSTTIME);



    cardinality = BN_CTX_get(ctx);

    lambda = BN_CTX_get(ctx);

    k = BN_CTX_get(ctx);

    if (k == NULL)

    if (k == NULL || !BN_mul(cardinality, group->order, group->cofactor, ctx))

        goto err;



    /*

     * Group orders are often on a word boundary.

     * Group cardinalities are often on a word boundary.

     * So when we pad the scalar, some timing diff might

     * pop if it needs to be expanded due to carries.

     * So expand ahead of time.

     */

    group_top = bn_get_top(group->order);

    cardinality_bits = BN_num_bits(cardinality);

    group_top = bn_get_top(cardinality);

    if ((bn_wexpand(k, group_top + 1) == NULL)

        || (bn_wexpand(lambda, group_top + 1) == NULL))

        goto err;
@@ -181,25 +182,25 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, 


    BN_set_flags(k, BN_FLG_CONSTTIME);



    if ((BN_num_bits(k) > order_bits) || (BN_is_negative(k))) {

    if ((BN_num_bits(k) > cardinality_bits) || (BN_is_negative(k))) {

        /*-

         * this is an unusual input, and we don't guarantee

         * constant-timeness

         */

        if (!BN_nnmod(k, k, group->order, ctx))

        if (!BN_nnmod(k, k, cardinality, ctx))

            goto err;

    }



    if (!BN_add(lambda, k, group->order))

    if (!BN_add(lambda, k, cardinality))

        goto err;

    BN_set_flags(lambda, BN_FLG_CONSTTIME);

    if (!BN_add(k, lambda, group->order))

    if (!BN_add(k, lambda, cardinality))

        goto err;

    /*

     * lambda := scalar + order

     * k := scalar + 2*order

     * lambda := scalar + cardinality

     * k := scalar + 2*cardinality

     */

    kbit = BN_is_bit_set(lambda, order_bits);

    kbit = BN_is_bit_set(lambda, cardinality_bits);

    BN_consttime_swap(kbit, k, lambda, group_top + 1);



    group_top = bn_get_top(group->field);
@@ -300,7 +301,7 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, 
     * This is XOR. pbit tracks the previous bit of k.

     */



    for (i = order_bits - 1; i >= 0; i--) {

    for (i = cardinality_bits - 1; i >= 0; i--) {

        kbit = BN_is_bit_set(k, i) ^ pbit;

        EC_POINT_CSWAP(kbit, r, s, group_top, Z_is_one);

        if (!EC_POINT_add(group, s, r, s, ctx))

test/recipes/30-test_evp_data/evppkey.txt

+29 −0
Original line number Diff line number Diff line
@@ -17257,6 +17257,35 @@ PeerKey=KAS-ECC-CDH_B-571_C24-Peer-PUBLIC 
Ctrl=ecdh_cofactor_mode:1

SharedSecret=02da266a269bdc8d8b2a0c6bb5762f102fc801c8d5394a9271539136bd81d4b69cfbb7525cd0a983fb7f7e9deec583b8f8e574c6184b2d79831ec770649e484dc006fa35b0bffd0b













# for cofactor-order points, ECC CDH (co-factor ECDH) should fail. Test that.

























PrivateKey=ALICE_cf_sect283k1













-----BEGIN PRIVATE KEY-----













MIGQAgEAMBAGByqGSM49AgEGBSuBBAAQBHkwdwIBAQQkAHtPwRfQZ9pWgSctyHdt













xt3pd8ESMI3ugVx8MDLkiVB8GkCRoUwDSgAEA+xpY5sDcgM2yYxoWOrzH7WUH+b3













n68A32kODgcKu8PXRYEKBH8Xzbr974982ZJW1sGrDs+P81sIFH8tdp45Jkr+OtfM













8uKr













-----END PRIVATE KEY-----

























PublicKey=ALICE_cf_sect283k1_PUB













-----BEGIN PUBLIC KEY-----













MF4wEAYHKoZIzj0CAQYFK4EEABADSgAEA+xpY5sDcgM2yYxoWOrzH7WUH+b3n68A













32kODgcKu8PXRYEKBH8Xzbr974982ZJW1sGrDs+P81sIFH8tdp45Jkr+OtfM8uKr













-----END PUBLIC KEY-----

























PublicKey=BOB_cf_sect283k1_PUB













-----BEGIN PUBLIC KEY-----













MF4wEAYHKoZIzj0CAQYFK4EEABADSgAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA













AAABAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAB













-----END PUBLIC KEY-----

























PrivPubKeyPair = ALICE_cf_sect283k1:ALICE_cf_sect283k1_PUB

























# ECDH Alice with Bob peer













Derive=ALICE_cf_sect283k1













PeerKey=BOB_cf_sect283k1_PUB













Ctrl=ecdh_cofactor_mode:1













Result = DERIVE_ERROR





























Title = Test keypair mistmatches