diff options
Diffstat (limited to 'crypto/bn/bn_exp.c')
| -rw-r--r-- | crypto/bn/bn_exp.c | 247 |
1 files changed, 244 insertions, 3 deletions
diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c index d6bb2b4397..d9b6c737fc 100644 --- a/crypto/bn/bn_exp.c +++ b/crypto/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 */ @@ -121,12 +122,20 @@ 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_CONSTTIME) != 0) + { + /* BN_FLG_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); else rr = r; - if ((v = BN_CTX_get(ctx)) == NULL) goto err; + v = BN_CTX_get(ctx); + if (rr == NULL || v == NULL) goto err; if (BN_copy(v,a) == NULL) goto err; bits=BN_num_bits(p); @@ -205,7 +214,7 @@ 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_CONSTTIME) == 0)) { BN_ULONG A = a->d[0]; ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL); @@ -237,6 +246,13 @@ 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_CONSTTIME) != 0) + { + /* BN_FLG_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) @@ -364,6 +380,11 @@ 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_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); @@ -495,6 +516,212 @@ 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_correct_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_correct_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) { @@ -519,6 +746,13 @@ 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_CONSTTIME) != 0) + { + /* BN_FLG_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); @@ -648,6 +882,13 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, /* Table of variables obtained from 'ctx' */ BIGNUM *val[TABLE_SIZE]; + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) + { + /* BN_FLG_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) |