Commit f667820c authored by Sohaib ul Hassan's avatar Sohaib ul Hassan Committed by Matt Caswell
Browse files

Implement coordinate blinding for EC_POINT 

This commit implements coordinate blinding, i.e., it randomizes the
representative of an elliptic curve point in its equivalence class, for
prime curves implemented through EC_GFp_simple_method,
EC_GFp_mont_method, and EC_GFp_nist_method.

This commit is derived from the patch
https://marc.info/?l=openssl-dev&m=131194808413635

 by Billy Brumley.

Coordinate blinding is a generally useful side-channel countermeasure
and is (mostly) free. The function itself takes a few field
multiplicationss, but is usually only necessary at the beginning of a
scalar multiplication (as implemented in the patch). When used this way,
it makes the values that variables take (i.e., field elements in an
algorithm state) unpredictable.

For instance, this mitigates chosen EC point side-channel attacks for
settings such as ECDH and EC private key decryption, for the
aforementioned curves.

For EC_METHODs using different coordinate representations this commit
does nothing, but the corresponding coordinate blinding function can be
easily added in the future to extend these changes to such curves.

Co-authored-by: default avatarNicola Tuveri <nic.tuv@gmail.com>
Co-authored-by: default avatarBilly Brumley <bbrumley@gmail.com>

Reviewed-by: default avatarAndy Polyakov <appro@openssl.org>
Reviewed-by: default avatarMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6501)
parent ddb634fe

CHANGES

+5 −0
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@@ -8,6 +8,11 @@ 
 release branch.















 Changes between 1.1.0h and 1.1.1 [xx XXX xxxx]













  *) Add coordinate blinding for EC_POINT and implement projective













     coordinate blinding for generic prime curves as a countermeasure to













     chosen point SCA attacks.













     [Sohaib ul Hassan, Nicola Tuveri, Billy Bob Brumley]



























  *) Add blinding to an ECDSA signature to protect against side channel attacks















     discovered by Keegan Ryan (NCC Group).















     [Matt Caswell]

































crypto/ec/ec2_smpl.c



+3
−1






























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@@ -64,7 +64,9 @@ const EC_METHOD *EC_GF2m_simple_method(void)













        ec_key_simple_generate_public_key,















        0, /* keycopy */















        0, /* keyfinish */













        ecdh_simple_compute_key













        ecdh_simple_compute_key,













        0, /* field_inverse_mod_ord */













        0  /* blind_coordinates */















    };































    return &ret;

































crypto/ec/ec_err.c



+2
−0






























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@@ -116,6 +116,8 @@ static const ERR_STRING_DATA EC_str_functs[] = {













     "ec_GFp_nist_field_sqr"},















    {ERR_PACK(ERR_LIB_EC, EC_F_EC_GFP_NIST_GROUP_SET_CURVE, 0),















     "ec_GFp_nist_group_set_curve"},













    {ERR_PACK(ERR_LIB_EC, EC_F_EC_GFP_SIMPLE_BLIND_COORDINATES, 0),













     "ec_GFp_simple_blind_coordinates"},















    {ERR_PACK(ERR_LIB_EC, EC_F_EC_GFP_SIMPLE_GROUP_CHECK_DISCRIMINANT, 0),















     "ec_GFp_simple_group_check_discriminant"},















    {ERR_PACK(ERR_LIB_EC, EC_F_EC_GFP_SIMPLE_GROUP_SET_CURVE, 0),

































crypto/ec/ec_lcl.h



+5
−0






























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@@ -176,6 +176,7 @@ struct ec_method_st {













    /* Inverse modulo order */















    int (*field_inverse_mod_ord)(const EC_GROUP *, BIGNUM *r, BIGNUM *x,















                                 BN_CTX *ctx);













    int (*blind_coordinates)(const EC_GROUP *group, EC_POINT *p, BN_CTX *ctx);















};































/*










@@ -382,6 +383,8 @@ int ec_GFp_simple_field_mul(const EC_GROUP *, BIGNUM *r, const BIGNUM *a,













                            const BIGNUM *b, BN_CTX *);















int ec_GFp_simple_field_sqr(const EC_GROUP *, BIGNUM *r, const BIGNUM *a,















                            BN_CTX *);













int ec_GFp_simple_blind_coordinates(const EC_GROUP *group, EC_POINT *p,













                                   BN_CTX *ctx);































/* method functions in ecp_mont.c */















int ec_GFp_mont_group_init(EC_GROUP *);










@@ -635,3 +638,5 @@ void X25519_public_from_private(uint8_t out_public_value[32],





























int EC_GROUP_do_inverse_ord(const EC_GROUP *group, BIGNUM *res,















                            BIGNUM *x, BN_CTX *ctx);



























int ec_point_blind_coordinates(const EC_GROUP *group, EC_POINT *p, BN_CTX *ctx);
























crypto/ec/ec_lib.c



+18
−0






























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@@ -1025,3 +1025,21 @@ int EC_GROUP_do_inverse_ord(const EC_GROUP *group, BIGNUM *res,













    else















        return 0;















}



























/*-













 * Coordinate blinding for EC_POINT.













 *













 * The underlying EC_METHOD can optionally implement this function:













 * underlying implementations should return 0 on errors, or 1 on













 * success.













 *













 * This wrapper returns 1 in case the underlying EC_METHOD does not













 * support coordinate blinding.













 */













int ec_point_blind_coordinates(const EC_GROUP *group, EC_POINT *p, BN_CTX *ctx)













{













    if (group->meth->blind_coordinates == NULL)













        return 1; /* ignore if not implemented */



























    return group->meth->blind_coordinates(group, p, ctx);













}