1 files changed, 242 insertions, 2 deletions

diff --git a/src/lib/libcrypto/bn/bn_exp.c b/src/lib/libcrypto/bn/bn_exp.c
index afdfd580fb..9e1e88abe8 100644
--- a/src/lib/libcrypto/bn/bn_exp.c
+++ b/src/lib/libcrypto/bn/bn_exp.c
@@ -56,7 +56,7 @@
  * [including the GNU Public Licence.]
  */
 /* ====================================================================
- * Copyright (c) 1998-2000 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -113,6 +113,7 @@
 #include "cryptlib.h"
 #include "bn_lcl.h"
 
+/* maximum precomputation table size for *variable* sliding windows */
 #define TABLE_SIZE      32
 
 /* this one works - simple but works */
@@ -121,6 +122,13 @@ int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
         int i,bits,ret=0;
         BIGNUM *v,*rr;
 
+        if (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) != 0)
+                {
+                /* BN_FLG_EXP_CONSTTIME only supported by BN_mod_exp_mont() */
+                BNerr(BN_F_BN_EXP,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
+                return -1;
+                }
+
         BN_CTX_start(ctx);
         if ((r == a) || (r == p))
                 rr = BN_CTX_get(ctx);
@@ -204,7 +212,7 @@ 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)
+                if (a->top == 1 && !a->neg && (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) == 0))
                         {
                         BN_ULONG A = a->d[0];
                         ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL);
@@ -234,6 +242,13 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
         BIGNUM val[TABLE_SIZE];
         BN_RECP_CTX recp;
 
+        if (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) != 0)
+                {
+                /* BN_FLG_EXP_CONSTTIME only supported by BN_mod_exp_mont() */
+                BNerr(BN_F_BN_MOD_EXP_RECP,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
+                return -1;
+                }
+
         bits=BN_num_bits(p);
 
         if (bits == 0)
@@ -361,6 +376,11 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
         BIGNUM val[TABLE_SIZE];
         BN_MONT_CTX *mont=NULL;
 
+        if (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) != 0)
+                {
+                return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
+                }
+
         bn_check_top(a);
         bn_check_top(p);
         bn_check_top(m);
@@ -493,6 +513,212 @@ err:
         return(ret);
         }
 
+
+/* BN_mod_exp_mont_consttime() stores the precomputed powers in a specific layout
+ * so that accessing any of these table values shows the same access pattern as far
+ * as cache lines are concerned.  The following functions are used to transfer a BIGNUM
+ * from/to that table. */
+
+static int MOD_EXP_CTIME_COPY_TO_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx, int width)
+        {
+        size_t i, j;
+
+        if (bn_wexpand(b, top) == NULL)
+                return 0;
+        while (b->top < top)
+                {
+                b->d[b->top++] = 0;
+                }
+        
+        for (i = 0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
+                {
+                buf[j] = ((unsigned char*)b->d)[i];
+                }
+
+        bn_fix_top(b);
+        return 1;
+        }
+
+static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx, int width)
+        {
+        size_t i, j;
+
+        if (bn_wexpand(b, top) == NULL)
+                return 0;
+
+        for (i=0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
+                {
+                ((unsigned char*)b->d)[i] = buf[j];
+                }
+
+        b->top = top;
+        bn_fix_top(b);
+        return 1;
+        }       
+
+/* Given a pointer value, compute the next address that is a cache line multiple. */
+#define MOD_EXP_CTIME_ALIGN(x_) \
+        ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((BN_ULONG)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
+
+/* This variant of BN_mod_exp_mont() uses fixed windows and the special
+ * precomputation memory layout to limit data-dependency to a minimum
+ * to protect secret exponents (cf. the hyper-threading timing attacks
+ * pointed out by Colin Percival,
+ * http://www.daemonology.net/hyperthreading-considered-harmful/)
+ */
+int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
+                    const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
+        {
+        int i,bits,ret=0,idx,window,wvalue;
+        int top;
+        BIGNUM *r;
+        const BIGNUM *aa;
+        BN_MONT_CTX *mont=NULL;
+
+        int numPowers;
+        unsigned char *powerbufFree=NULL;
+        int powerbufLen = 0;
+        unsigned char *powerbuf=NULL;
+        BIGNUM *computeTemp=NULL, *am=NULL;
+
+        bn_check_top(a);
+        bn_check_top(p);
+        bn_check_top(m);
+
+        top = m->top;
+
+        if (!(m->d[0] & 1))
+                {
+                BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME,BN_R_CALLED_WITH_EVEN_MODULUS);
+                return(0);
+                }
+        bits=BN_num_bits(p);
+        if (bits == 0)
+                {
+                ret = BN_one(rr);
+                return ret;
+                }
+
+        /* Initialize BIGNUM context and allocate intermediate result */
+        BN_CTX_start(ctx);
+        r = BN_CTX_get(ctx);
+        if (r == NULL) goto err;
+
+        /* Allocate a montgomery context if it was not supplied by the caller.
+         * If this is not done, things will break in the montgomery part.
+         */
+        if (in_mont != NULL)
+                mont=in_mont;
+        else
+                {
+                if ((mont=BN_MONT_CTX_new()) == NULL) goto err;
+                if (!BN_MONT_CTX_set(mont,m,ctx)) goto err;
+                }
+
+        /* Get the window size to use with size of p. */
+        window = BN_window_bits_for_ctime_exponent_size(bits);
+
+        /* Allocate a buffer large enough to hold all of the pre-computed
+         * powers of a.
+         */
+        numPowers = 1 << window;
+        powerbufLen = sizeof(m->d[0])*top*numPowers;
+        if ((powerbufFree=(unsigned char*)OPENSSL_malloc(powerbufLen+MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH)) == NULL)
+                goto err;
+                
+        powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
+        memset(powerbuf, 0, powerbufLen);
+
+        /* Initialize the intermediate result. Do this early to save double conversion,
+         * once each for a^0 and intermediate result.
+         */
+        if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
+        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(r, top, powerbuf, 0, numPowers)) goto err;
+
+        /* Initialize computeTemp as a^1 with montgomery precalcs */
+        computeTemp = BN_CTX_get(ctx);
+        am = BN_CTX_get(ctx);
+        if (computeTemp==NULL || am==NULL) goto err;
+
+        if (a->neg || BN_ucmp(a,m) >= 0)
+                {
+                if (!BN_mod(am,a,m,ctx))
+                        goto err;
+                aa= am;
+                }
+        else
+                aa=a;
+        if (!BN_to_montgomery(am,aa,mont,ctx)) goto err;
+        if (!BN_copy(computeTemp, am)) goto err;
+        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(am, top, powerbuf, 1, numPowers)) goto err;
+
+        /* If the window size is greater than 1, then calculate
+         * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1)
+         * (even powers could instead be computed as (a^(i/2))^2
+         * to use the slight performance advantage of sqr over mul).
+         */
+        if (window > 1)
+                {
+                for (i=2; i<numPowers; i++)
+                        {
+                        /* Calculate a^i = a^(i-1) * a */
+                        if (!BN_mod_mul_montgomery(computeTemp,am,computeTemp,mont,ctx))
+                                goto err;
+                        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(computeTemp, top, powerbuf, i, numPowers)) goto err;
+                        }
+                }
+
+        /* Adjust the number of bits up to a multiple of the window size.
+         * If the exponent length is not a multiple of the window size, then
+         * this pads the most significant bits with zeros to normalize the
+         * scanning loop to there's no special cases.
+         *
+         * * NOTE: Making the window size a power of two less than the native
+         * * word size ensures that the padded bits won't go past the last
+         * * word in the internal BIGNUM structure. Going past the end will
+         * * still produce the correct result, but causes a different branch
+         * * to be taken in the BN_is_bit_set function.
+         */
+        bits = ((bits+window-1)/window)*window;
+        idx=bits-1;     /* The top bit of the window */
+
+        /* Scan the exponent one window at a time starting from the most
+         * significant bits.
+         */
+        while (idx >= 0)
+                {
+                wvalue=0; /* The 'value' of the window */
+                
+                /* Scan the window, squaring the result as we go */
+                for (i=0; i<window; i++,idx--)
+                        {
+                        if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))     goto err;
+                        wvalue = (wvalue<<1)+BN_is_bit_set(p,idx);
+                        }
+                
+                /* Fetch the appropriate pre-computed value from the pre-buf */
+                if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(computeTemp, top, powerbuf, wvalue, numPowers)) goto err;
+
+                /* Multiply the result into the intermediate result */
+                if (!BN_mod_mul_montgomery(r,r,computeTemp,mont,ctx)) goto err;
+                }
+
+        /* Convert the final result from montgomery to standard format */
+        if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
+        ret=1;
+err:
+        if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
+        if (powerbuf!=NULL)
+                {
+                OPENSSL_cleanse(powerbuf,powerbufLen);
+                OPENSSL_free(powerbufFree);
+                }
+        if (am!=NULL) BN_clear(am);
+        if (computeTemp!=NULL) BN_clear(computeTemp);
+        BN_CTX_end(ctx);
+        return(ret);
+        }
+
 int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
         {
@@ -517,6 +743,13 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
                 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
 
+        if (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) != 0)
+                {
+                /* BN_FLG_EXP_CONSTTIME only supported by BN_mod_exp_mont() */
+                BNerr(BN_F_BN_MOD_EXP_MONT_WORD,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
+                return -1;
+                }
+
         bn_check_top(p);
         bn_check_top(m);
 
@@ -644,6 +877,13 @@ int BN_mod_exp_simple(BIGNUM *r,
         BIGNUM *d;
         BIGNUM val[TABLE_SIZE];
 
+        if (BN_get_flags(p, BN_FLG_EXP_CONSTTIME) != 0)
+                {
+                /* BN_FLG_EXP_CONSTTIME only supported by BN_mod_exp_mont() */
+                BNerr(BN_F_BN_MOD_EXP_SIMPLE,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
+                return -1;
+                }
+
         bits=BN_num_bits(p);
 
         if (bits == 0)