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Diffstat (limited to 'crypto/bn/bn_gcd.c')
-rw-r--r--crypto/bn/bn_gcd.c386
1 files changed, 201 insertions, 185 deletions
diff --git a/crypto/bn/bn_gcd.c b/crypto/bn/bn_gcd.c
index ef81acb77ba6..0941f7b97f3f 100644
--- a/crypto/bn/bn_gcd.c
+++ b/crypto/bn/bn_gcd.c
@@ -1,5 +1,5 @@
/*
- * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
@@ -10,22 +10,189 @@
#include "internal/cryptlib.h"
#include "bn_local.h"
-/* solves ax == 1 (mod n) */
-static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *in,
- const BIGNUM *a, const BIGNUM *n,
- BN_CTX *ctx);
-
-BIGNUM *BN_mod_inverse(BIGNUM *in,
- const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
+/*
+ * bn_mod_inverse_no_branch is a special version of BN_mod_inverse. It does
+ * not contain branches that may leak sensitive information.
+ *
+ * This is a static function, we ensure all callers in this file pass valid
+ * arguments: all passed pointers here are non-NULL.
+ */
+static ossl_inline
+BIGNUM *bn_mod_inverse_no_branch(BIGNUM *in,
+ const BIGNUM *a, const BIGNUM *n,
+ BN_CTX *ctx, int *pnoinv)
{
- BIGNUM *rv;
- int noinv;
- rv = int_bn_mod_inverse(in, a, n, ctx, &noinv);
- if (noinv)
- BNerr(BN_F_BN_MOD_INVERSE, BN_R_NO_INVERSE);
- return rv;
+ BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
+ BIGNUM *ret = NULL;
+ int sign;
+
+ bn_check_top(a);
+ bn_check_top(n);
+
+ BN_CTX_start(ctx);
+ A = BN_CTX_get(ctx);
+ B = BN_CTX_get(ctx);
+ X = BN_CTX_get(ctx);
+ D = BN_CTX_get(ctx);
+ M = BN_CTX_get(ctx);
+ Y = BN_CTX_get(ctx);
+ T = BN_CTX_get(ctx);
+ if (T == NULL)
+ goto err;
+
+ if (in == NULL)
+ R = BN_new();
+ else
+ R = in;
+ if (R == NULL)
+ goto err;
+
+ BN_one(X);
+ BN_zero(Y);
+ if (BN_copy(B, a) == NULL)
+ goto err;
+ if (BN_copy(A, n) == NULL)
+ goto err;
+ A->neg = 0;
+
+ if (B->neg || (BN_ucmp(B, A) >= 0)) {
+ /*
+ * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+ * BN_div_no_branch will be called eventually.
+ */
+ {
+ BIGNUM local_B;
+ bn_init(&local_B);
+ BN_with_flags(&local_B, B, BN_FLG_CONSTTIME);
+ if (!BN_nnmod(B, &local_B, A, ctx))
+ goto err;
+ /* Ensure local_B goes out of scope before any further use of B */
+ }
+ }
+ sign = -1;
+ /*-
+ * From B = a mod |n|, A = |n| it follows that
+ *
+ * 0 <= B < A,
+ * -sign*X*a == B (mod |n|),
+ * sign*Y*a == A (mod |n|).
+ */
+
+ while (!BN_is_zero(B)) {
+ BIGNUM *tmp;
+
+ /*-
+ * 0 < B < A,
+ * (*) -sign*X*a == B (mod |n|),
+ * sign*Y*a == A (mod |n|)
+ */
+
+ /*
+ * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+ * BN_div_no_branch will be called eventually.
+ */
+ {
+ BIGNUM local_A;
+ bn_init(&local_A);
+ BN_with_flags(&local_A, A, BN_FLG_CONSTTIME);
+
+ /* (D, M) := (A/B, A%B) ... */
+ if (!BN_div(D, M, &local_A, B, ctx))
+ goto err;
+ /* Ensure local_A goes out of scope before any further use of A */
+ }
+
+ /*-
+ * Now
+ * A = D*B + M;
+ * thus we have
+ * (**) sign*Y*a == D*B + M (mod |n|).
+ */
+
+ tmp = A; /* keep the BIGNUM object, the value does not
+ * matter */
+
+ /* (A, B) := (B, A mod B) ... */
+ A = B;
+ B = M;
+ /* ... so we have 0 <= B < A again */
+
+ /*-
+ * Since the former M is now B and the former B is now A,
+ * (**) translates into
+ * sign*Y*a == D*A + B (mod |n|),
+ * i.e.
+ * sign*Y*a - D*A == B (mod |n|).
+ * Similarly, (*) translates into
+ * -sign*X*a == A (mod |n|).
+ *
+ * Thus,
+ * sign*Y*a + D*sign*X*a == B (mod |n|),
+ * i.e.
+ * sign*(Y + D*X)*a == B (mod |n|).
+ *
+ * So if we set (X, Y, sign) := (Y + D*X, X, -sign), we arrive back at
+ * -sign*X*a == B (mod |n|),
+ * sign*Y*a == A (mod |n|).
+ * Note that X and Y stay non-negative all the time.
+ */
+
+ if (!BN_mul(tmp, D, X, ctx))
+ goto err;
+ if (!BN_add(tmp, tmp, Y))
+ goto err;
+
+ M = Y; /* keep the BIGNUM object, the value does not
+ * matter */
+ Y = X;
+ X = tmp;
+ sign = -sign;
+ }
+
+ /*-
+ * The while loop (Euclid's algorithm) ends when
+ * A == gcd(a,n);
+ * we have
+ * sign*Y*a == A (mod |n|),
+ * where Y is non-negative.
+ */
+
+ if (sign < 0) {
+ if (!BN_sub(Y, n, Y))
+ goto err;
+ }
+ /* Now Y*a == A (mod |n|). */
+
+ if (BN_is_one(A)) {
+ /* Y*a == 1 (mod |n|) */
+ if (!Y->neg && BN_ucmp(Y, n) < 0) {
+ if (!BN_copy(R, Y))
+ goto err;
+ } else {
+ if (!BN_nnmod(R, Y, n, ctx))
+ goto err;
+ }
+ } else {
+ *pnoinv = 1;
+ /* caller sets the BN_R_NO_INVERSE error */
+ goto err;
+ }
+
+ ret = R;
+ *pnoinv = 0;
+
+ err:
+ if ((ret == NULL) && (in == NULL))
+ BN_free(R);
+ BN_CTX_end(ctx);
+ bn_check_top(ret);
+ return ret;
}
+/*
+ * This is an internal function, we assume all callers pass valid arguments:
+ * all pointers passed here are assumed non-NULL.
+ */
BIGNUM *int_bn_mod_inverse(BIGNUM *in,
const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx,
int *pnoinv)
@@ -36,17 +203,15 @@ BIGNUM *int_bn_mod_inverse(BIGNUM *in,
/* This is invalid input so we don't worry about constant time here */
if (BN_abs_is_word(n, 1) || BN_is_zero(n)) {
- if (pnoinv != NULL)
- *pnoinv = 1;
+ *pnoinv = 1;
return NULL;
}
- if (pnoinv != NULL)
- *pnoinv = 0;
+ *pnoinv = 0;
if ((BN_get_flags(a, BN_FLG_CONSTTIME) != 0)
|| (BN_get_flags(n, BN_FLG_CONSTTIME) != 0)) {
- return BN_mod_inverse_no_branch(in, a, n, ctx);
+ return bn_mod_inverse_no_branch(in, a, n, ctx, pnoinv);
}
bn_check_top(a);
@@ -332,8 +497,7 @@ BIGNUM *int_bn_mod_inverse(BIGNUM *in,
goto err;
}
} else {
- if (pnoinv)
- *pnoinv = 1;
+ *pnoinv = 1;
goto err;
}
ret = R;
@@ -345,175 +509,27 @@ BIGNUM *int_bn_mod_inverse(BIGNUM *in,
return ret;
}
-/*
- * BN_mod_inverse_no_branch is a special version of BN_mod_inverse. It does
- * not contain branches that may leak sensitive information.
- */
-static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *in,
- const BIGNUM *a, const BIGNUM *n,
- BN_CTX *ctx)
+/* solves ax == 1 (mod n) */
+BIGNUM *BN_mod_inverse(BIGNUM *in,
+ const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
{
- BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
- BIGNUM *ret = NULL;
- int sign;
-
- bn_check_top(a);
- bn_check_top(n);
-
- BN_CTX_start(ctx);
- A = BN_CTX_get(ctx);
- B = BN_CTX_get(ctx);
- X = BN_CTX_get(ctx);
- D = BN_CTX_get(ctx);
- M = BN_CTX_get(ctx);
- Y = BN_CTX_get(ctx);
- T = BN_CTX_get(ctx);
- if (T == NULL)
- goto err;
-
- if (in == NULL)
- R = BN_new();
- else
- R = in;
- if (R == NULL)
- goto err;
-
- BN_one(X);
- BN_zero(Y);
- if (BN_copy(B, a) == NULL)
- goto err;
- if (BN_copy(A, n) == NULL)
- goto err;
- A->neg = 0;
-
- if (B->neg || (BN_ucmp(B, A) >= 0)) {
- /*
- * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
- * BN_div_no_branch will be called eventually.
- */
- {
- BIGNUM local_B;
- bn_init(&local_B);
- BN_with_flags(&local_B, B, BN_FLG_CONSTTIME);
- if (!BN_nnmod(B, &local_B, A, ctx))
- goto err;
- /* Ensure local_B goes out of scope before any further use of B */
- }
- }
- sign = -1;
- /*-
- * From B = a mod |n|, A = |n| it follows that
- *
- * 0 <= B < A,
- * -sign*X*a == B (mod |n|),
- * sign*Y*a == A (mod |n|).
- */
-
- while (!BN_is_zero(B)) {
- BIGNUM *tmp;
-
- /*-
- * 0 < B < A,
- * (*) -sign*X*a == B (mod |n|),
- * sign*Y*a == A (mod |n|)
- */
-
- /*
- * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
- * BN_div_no_branch will be called eventually.
- */
- {
- BIGNUM local_A;
- bn_init(&local_A);
- BN_with_flags(&local_A, A, BN_FLG_CONSTTIME);
+ BN_CTX *new_ctx = NULL;
+ BIGNUM *rv;
+ int noinv = 0;
- /* (D, M) := (A/B, A%B) ... */
- if (!BN_div(D, M, &local_A, B, ctx))
- goto err;
- /* Ensure local_A goes out of scope before any further use of A */
+ if (ctx == NULL) {
+ ctx = new_ctx = BN_CTX_new();
+ if (ctx == NULL) {
+ BNerr(BN_F_BN_MOD_INVERSE, ERR_R_MALLOC_FAILURE);
+ return NULL;
}
-
- /*-
- * Now
- * A = D*B + M;
- * thus we have
- * (**) sign*Y*a == D*B + M (mod |n|).
- */
-
- tmp = A; /* keep the BIGNUM object, the value does not
- * matter */
-
- /* (A, B) := (B, A mod B) ... */
- A = B;
- B = M;
- /* ... so we have 0 <= B < A again */
-
- /*-
- * Since the former M is now B and the former B is now A,
- * (**) translates into
- * sign*Y*a == D*A + B (mod |n|),
- * i.e.
- * sign*Y*a - D*A == B (mod |n|).
- * Similarly, (*) translates into
- * -sign*X*a == A (mod |n|).
- *
- * Thus,
- * sign*Y*a + D*sign*X*a == B (mod |n|),
- * i.e.
- * sign*(Y + D*X)*a == B (mod |n|).
- *
- * So if we set (X, Y, sign) := (Y + D*X, X, -sign), we arrive back at
- * -sign*X*a == B (mod |n|),
- * sign*Y*a == A (mod |n|).
- * Note that X and Y stay non-negative all the time.
- */
-
- if (!BN_mul(tmp, D, X, ctx))
- goto err;
- if (!BN_add(tmp, tmp, Y))
- goto err;
-
- M = Y; /* keep the BIGNUM object, the value does not
- * matter */
- Y = X;
- X = tmp;
- sign = -sign;
- }
-
- /*-
- * The while loop (Euclid's algorithm) ends when
- * A == gcd(a,n);
- * we have
- * sign*Y*a == A (mod |n|),
- * where Y is non-negative.
- */
-
- if (sign < 0) {
- if (!BN_sub(Y, n, Y))
- goto err;
}
- /* Now Y*a == A (mod |n|). */
- if (BN_is_one(A)) {
- /* Y*a == 1 (mod |n|) */
- if (!Y->neg && BN_ucmp(Y, n) < 0) {
- if (!BN_copy(R, Y))
- goto err;
- } else {
- if (!BN_nnmod(R, Y, n, ctx))
- goto err;
- }
- } else {
- BNerr(BN_F_BN_MOD_INVERSE_NO_BRANCH, BN_R_NO_INVERSE);
- goto err;
- }
- ret = R;
- err:
- if ((ret == NULL) && (in == NULL))
- BN_free(R);
- BN_CTX_end(ctx);
- bn_check_top(ret);
- return ret;
+ rv = int_bn_mod_inverse(in, a, n, ctx, &noinv);
+ if (noinv)
+ BNerr(BN_F_BN_MOD_INVERSE, BN_R_NO_INVERSE);
+ BN_CTX_free(new_ctx);
+ return rv;
}
/*-
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-19 20:24:06 +0000