Add a comment to explain the purpose of bn_cmp_part_words().

[openssl.git] / crypto / bn / bn_exp.c

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 35ab56efc04d6b1ab90cb1fbdb5e0e910dfac7e4..1739be68645b4af678d6609ead457b0df05d1765 100644 (file)
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -191,6 +191,7 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
         */
 
 #define MONT_MUL_MOD
+#define MONT_EXP_WORD
 #define RECP_MUL_MOD
 
 #ifdef MONT_MUL_MOD
@@ -202,12 +203,14 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 
        if (BN_is_odd(m))
                {
+#  ifdef MONT_EXP_WORD
                if (a->top == 1 && !a->neg)
                        {
                        BN_ULONG A = a->d[0];
                        ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL);
                        }
                else
+#  endif
                        ret=BN_mod_exp_mont(r,a,p,m,ctx,NULL);
                }
        else
@@ -235,8 +238,8 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 
        if (bits == 0)
                {
-               BN_one(r);
-               return(1);
+               ret = BN_one(r);
+               return ret;
                }
 
        BN_CTX_start(ctx);
@@ -249,6 +252,11 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
        ts=1;
 
        if (!BN_nnmod(&(val[0]),a,m,ctx)) goto err;             /* 1 */
+       if (BN_is_zero(&(val[0])))
+               {
+               ret = BN_zero(r);
+               goto err;
+               }
 
        window = BN_window_bits_for_exponent_size(bits);
        if (window > 1)
@@ -355,9 +363,10 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
        bits=BN_num_bits(p);
        if (bits == 0)
                {
-               BN_one(rr);
-               return(1);
+               ret = BN_one(rr);
+               return ret;
                }
+
        BN_CTX_start(ctx);
        d = BN_CTX_get(ctx);
        r = BN_CTX_get(ctx);
@@ -384,6 +393,11 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
                }
        else
                aa=a;
+       if (BN_is_zero(aa))
+               {
+               ret = BN_zero(rr);
+               goto err;
+               }
        if (!BN_to_montgomery(&(val[0]),aa,mont,ctx)) goto err; /* 1 */
 
        window = BN_window_bits_for_exponent_size(bits);
@@ -492,17 +506,26 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
        bn_check_top(p);
        bn_check_top(m);
 
-       if (!(m->d[0] & 1))
+       if (m->top == 0 || !(m->d[0] & 1))
                {
                BNerr(BN_F_BN_MOD_EXP_MONT_WORD,BN_R_CALLED_WITH_EVEN_MODULUS);
                return(0);
                }
+       if (m->top == 1)
+               a %= m->d[0]; /* make sure that 'a' is reduced */
+
        bits = BN_num_bits(p);
        if (bits == 0)
                {
-               BN_one(rr);
-               return(1);
+               ret = BN_one(rr);
+               return ret;
+               }
+       if (a == 0)
+               {
+               ret = BN_zero(rr);
+               return ret;
                }
+
        BN_CTX_start(ctx);
        d = BN_CTX_get(ctx);
        r = BN_CTX_get(ctx);
@@ -611,8 +634,8 @@ int BN_mod_exp_simple(BIGNUM *r,
 
        if (bits == 0)
                {
-               BN_one(r);
-               return(1);
+               ret = BN_one(r);
+               return ret;
                }
 
        BN_CTX_start(ctx);
@@ -621,6 +644,11 @@ int BN_mod_exp_simple(BIGNUM *r,
        BN_init(&(val[0]));
        ts=1;
        if (!BN_nnmod(&(val[0]),a,m,ctx)) goto err;             /* 1 */
+       if (BN_is_zero(&(val[0])))
+               {
+               ret = BN_zero(r);
+               goto err;
+               }
 
        window = BN_window_bits_for_exponent_size(bits);
        if (window > 1)