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Change BN_mod_sqrt() so that it verifies that the input value is

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really the square of the return value.
This commit is contained in:
Bodo Möller 2002-08-02 14:57:53 +00:00
parent 5af7d1a3b8
commit 6fb60a84dd
3 changed files with 37 additions and 20 deletions
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5
CHANGES
View File

@ -4,6 +4,11 @@
Changes between 0.9.7 and 0.9.8 [xx XXX 2002]
*) Change BN_mod_sqrt() so that it verifies that the input value
is really the square of the return value. (Previously,
BN_mod_sqrt would show GIGO behaviour.)
[Bodo Moeller]
*) Add named elliptic curves over binary fields from X9.62, SECG,
and WAP/WTLS; add OIDs that were still missing.

49
crypto/bn/bn_sqrt.c
View File

@ -72,7 +72,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
BIGNUM *ret = in;
int err = 1;
int r;
BIGNUM *b, *q, *t, *x, *y;
BIGNUM *A, *b, *q, *t, *x, *y;
int e, i, j;
if (!BN_is_odd(p) || BN_abs_is_word(p, 1))
@ -120,6 +120,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
#endif
BN_CTX_start(ctx);
A = BN_CTX_get(ctx);
b = BN_CTX_get(ctx);
q = BN_CTX_get(ctx);
t = BN_CTX_get(ctx);
@ -131,6 +132,9 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
ret = BN_new();
if (ret == NULL) goto end;
/* A = a mod p */
if (!BN_nnmod(A, a, p, ctx)) goto end;
/* now write |p| - 1 as 2^e*q where q is odd */
e = 1;
while (!BN_is_bit_set(p, e))
@ -149,9 +153,9 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
if (!BN_rshift(q, p, 2)) goto end;
q->neg = 0;
if (!BN_add_word(q, 1)) goto end;
if (!BN_mod_exp(ret, a, q, p, ctx)) goto end;
if (!BN_mod_exp(ret, A, q, p, ctx)) goto end;
err = 0;
goto end;
goto vrfy;
}
if (e == 2)
@ -182,15 +186,8 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
* November 1992.)
*/
/* make sure that a is reduced modulo p */
if (a->neg || BN_ucmp(a, p) >= 0)
{
if (!BN_nnmod(x, a, p, ctx)) goto end;
a = x; /* use x as temporary variable */
}
/* t := 2*a */
if (!BN_mod_lshift1_quick(t, a, p)) goto end;
if (!BN_mod_lshift1_quick(t, A, p)) goto end;
/* b := (2*a)^((|p|-5)/8) */
if (!BN_rshift(q, p, 3)) goto end;
@ -205,12 +202,12 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
if (!BN_sub_word(t, 1)) goto end;
/* x = a*b*t */
if (!BN_mod_mul(x, a, b, p, ctx)) goto end;
if (!BN_mod_mul(x, A, b, p, ctx)) goto end;
if (!BN_mod_mul(x, x, t, p, ctx)) goto end;
if (!BN_copy(ret, x)) goto end;
err = 0;
goto end;
goto vrfy;
}
/* e > 2, so we really have to use the Tonelli/Shanks algorithm.
@ -297,7 +294,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
/* x := a^((q-1)/2) */
if (BN_is_zero(t)) /* special case: p = 2^e + 1 */
{
if (!BN_nnmod(t, a, p, ctx)) goto end;
if (!BN_nnmod(t, A, p, ctx)) goto end;
if (BN_is_zero(t))
{
/* special case: a == 0 (mod p) */
@ -310,7 +307,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
}
else
{
if (!BN_mod_exp(x, a, t, p, ctx)) goto end;
if (!BN_mod_exp(x, A, t, p, ctx)) goto end;
if (BN_is_zero(x))
{
/* special case: a == 0 (mod p) */
@ -322,10 +319,10 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
/* b := a*x^2 (= a^q) */
if (!BN_mod_sqr(b, x, p, ctx)) goto end;
if (!BN_mod_mul(b, b, a, p, ctx)) goto end;
if (!BN_mod_mul(b, b, A, p, ctx)) goto end;
/* x := a*x (= a^((q+1)/2)) */
if (!BN_mod_mul(x, x, a, p, ctx)) goto end;
if (!BN_mod_mul(x, x, A, p, ctx)) goto end;
while (1)
{
@ -342,7 +339,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
{
if (!BN_copy(ret, x)) goto end;
err = 0;
goto end;
goto vrfy;
}
@ -373,6 +370,22 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
e = i;
}
vrfy:
if (!err)
{
/* verify the result -- the input might have been not a square
* (test added in 0.9.8) */
if (!BN_mod_sqr(x, ret, p, ctx))
err = 1;
if (!err && 0 != BN_cmp(x, A))
{
BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE);
err = 1;
}
}
end:
if (err)
{

3
crypto/ec/ecp_smpl.c
View File

@ -705,8 +705,6 @@ int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *po
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, ERR_R_BN_LIB);
goto err;
}
/* If tmp1 is not a square (i.e. there is no point on the curve with
* our x), then y now is a nonsense value too */
if (y_bit != BN_is_odd(y))
{
@ -720,6 +718,7 @@ int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *po
if (kron == 1)
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSION_BIT);
else
/* BN_mod_sqrt() should have cought this error (not a square) */
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSED_POINT);
goto err;
}