From 5cf5f6e9ac953270c696c1f4bd01881d183be5e3 Mon Sep 17 00:00:00 2001 From: cinap_lenrek Date: Sun, 31 Dec 2017 10:59:01 +0100 Subject: libmp: use constant time encode(2) routines instead of lookup tables the encode(2) routines are constant time now, so use them instead of using lookup table that can leak information through cache timing side channel. --- sys/src/libmp/port/mpfmt.c | 4 +-- sys/src/libmp/port/strtomp.c | 76 +++++++++----------------------------------- 2 files changed, 16 insertions(+), 64 deletions(-) diff --git a/sys/src/libmp/port/mpfmt.c b/sys/src/libmp/port/mpfmt.c index 837f6f87a..e1dd74267 100644 --- a/sys/src/libmp/port/mpfmt.c +++ b/sys/src/libmp/port/mpfmt.c @@ -17,8 +17,6 @@ toencx(mpint *b, char *buf, int len, int (*enc)(char*, int, uchar*, int)) return rv; } -static char set16[] = "0123456789ABCDEF"; - static int topow2(mpint *b, char *buf, int len, int s) { @@ -39,7 +37,7 @@ topow2(mpint *b, char *buf, int len, int s) if(j != 0 || out != buf){ if(out >= eout) return -1; - *out++ = set16[j]; + *out++ = enc16chr(j); } } } diff --git a/sys/src/libmp/port/strtomp.c b/sys/src/libmp/port/strtomp.c index b0b7d2898..56f70845c 100644 --- a/sys/src/libmp/port/strtomp.c +++ b/sys/src/libmp/port/strtomp.c @@ -2,58 +2,16 @@ #include #include "dat.h" -static struct { - int inited; - - uchar t64[256]; - uchar t32[256]; - uchar t16[256]; - uchar t10[256]; -} tab; - -enum { - INVAL= 255 -}; - -static char set64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; -static char set32[] = "23456789abcdefghijkmnpqrstuvwxyz"; -static char set16[] = "0123456789ABCDEF0123456789abcdef"; -static char set10[] = "0123456789"; - -static void -init(void) -{ - char *p; - - memset(tab.t64, INVAL, sizeof(tab.t64)); - memset(tab.t32, INVAL, sizeof(tab.t32)); - memset(tab.t16, INVAL, sizeof(tab.t16)); - memset(tab.t10, INVAL, sizeof(tab.t10)); - - for(p = set64; *p; p++) - tab.t64[*p] = p-set64; - for(p = set32; *p; p++) - tab.t32[*p] = p-set32; - for(p = set16; *p; p++) - tab.t16[*p] = (p-set16)%16; - for(p = set10; *p; p++) - tab.t10[*p] = (p-set10); - - tab.inited = 1; -} - static char* frompow2(char *a, mpint *b, int s) { char *p, *next; - int i; mpdigit x; - int sn; + int i; - sn = 1<= sn) - break; + i = 1<top = 0; @@ -64,7 +22,7 @@ frompow2(char *a, mpint *b, int s) for(i = 0; i < Dbits; i += s){ if(p <= a) break; - x |= tab.t16[*(uchar*)--p]<p[b->top++] = x; } @@ -78,9 +36,8 @@ from8(char *a, mpint *b) mpdigit x, y; int i; - for(p = a; *p; p++) - if(tab.t10[*(uchar*)p] >= 8) - break; + for(p = a; ((*p - '0') & 255) < 8; p++) + ; mpbits(b, (p-a)*3); b->top = 0; @@ -89,7 +46,7 @@ from8(char *a, mpint *b) i = 0; x = y = 0; while(p > a){ - y = tab.t10[*(uchar*)--p]; + y = *--p - '0'; x |= y << i; i += 3; if(i >= Dbits){ @@ -124,8 +81,8 @@ from10(char *a, mpint *b) // do a billion at a time in native arithmetic x = 0; for(i = 0; i < 9; i++){ - y = tab.t10[*(uchar*)a]; - if(y == INVAL) + y = *a - '0'; + if(y > 9) break; a++; x *= 10; @@ -139,7 +96,7 @@ from10(char *a, mpint *b) uitomp(x, r); mpmul(b, pow, b); mpadd(b, r, b); - if(i != 9) + if(i < 9) break; } mpfree(pow); @@ -148,14 +105,14 @@ from10(char *a, mpint *b) } static char* -fromdecx(char *a, mpint *b, uchar tab[256], int (*dec)(uchar*, int, char*, int)) +fromdecx(char *a, mpint *b, int (*chr)(int), int (*dec)(uchar*, int, char*, int)) { char *buf = a; uchar *p; int n, m; b->top = 0; - for(; tab[*(uchar*)a] != INVAL; a++) + for(; (*chr)(*a) >= 0; a++) ; n = a-buf; if(n > 0){ @@ -181,9 +138,6 @@ strtomp(char *a, char **pp, int base, mpint *b) setmalloctag(b, getcallerpc(&a)); } - if(tab.inited == 0) - init(); - while(*a==' ' || *a=='\t') a++; @@ -230,10 +184,10 @@ strtomp(char *a, char **pp, int base, mpint *b) e = frompow2(a, b, 4); break; case 32: - e = fromdecx(a, b, tab.t32, dec32); + e = fromdecx(a, b, dec32chr, dec32); break; case 64: - e = fromdecx(a, b, tab.t64, dec64); + e = fromdecx(a, b, dec64chr, dec64); break; default: abort(); -- cgit v1.2.3