libc: constant time implementation for encode(2) routines, fix base32

the string encoding functions touch secret key material
in a bunch of places (devtls, devcap), so make sure we do
not leak information by cache timing side channels, making
the encoding and decoding routines constant time.

we also expose the alphabets through encXchr()/decXchr()
functions so caller can find the end of a encoded string
before calling decode function (for libmp).

the base32 encoding was broken in several ways. inputs
lengths of len%5 == [2,3,4] had output truncated and
it was using non-standard alphabet. documenting the alphabet
change in the manpage.

4 files changed, 129 insertions, 87 deletions

diff --git a/sys/src/libc/port/encodefmt.c b/sys/src/libc/port/encodefmt.c
index 721a58c9f..92cc4154a 100644
--- a/sys/src/libc/port/encodefmt.c
+++ b/sys/src/libc/port/encodefmt.c
@@ -48,17 +48,14 @@ encodefmt(Fmt *f)
 	// convert
 	out = buf;
 	switch(f->r){
-	case '<':
-		rv = enc32(out, len, b, ilen);
-		break;
 	case '[':
 		rv = enc64(out, len, b, ilen);
 		break;
+	case '<':
+		rv = enc32(out, len, b, ilen);
+		break;
 	case 'H':
 		rv = enc16(out, len, b, ilen);
-		if(rv >= 0 && (f->flags & FmtLong))
-			for(p = buf; *p; p++)
-				*p = tolower(*p);
 		break;
 	default:
 		rv = -1;
@@ -67,6 +64,10 @@ encodefmt(Fmt *f)
 	if(rv < 0)
 		goto error;
 
+	if((f->flags & FmtLong) != 0 && f->r != '[')
+		for(p = buf; *p; p++)
+			*p = tolower(*p);
+
 	fmtstrcpy(f, buf);
 	if(buf != obuf)
 		free(buf);
diff --git a/sys/src/libc/port/u16.c b/sys/src/libc/port/u16.c
index 4e1637120..60ffa72c8 100644
--- a/sys/src/libc/port/u16.c
+++ b/sys/src/libc/port/u16.c
@@ -1,6 +1,28 @@
 #include <u.h>
 #include <libc.h>
-static char t16e[] = "0123456789ABCDEF";
+
+#define between(x,min,max)	(((min-1-x) & (x-max-1))>>8)
+
+int
+enc16chr(int o)
+{
+	int c;
+
+	c  = between(o,  0,  9) & ('0'+o);
+	c |= between(o, 10, 15) & ('A'+(o-10));
+	return c;
+}
+
+int
+dec16chr(int c)
+{
+	int o;
+
+	o  = between(c, '0', '9') & (1+(c-'0'));
+	o |= between(c, 'A', 'F') & (1+10+(c-'A'));
+	o |= between(c, 'a', 'f') & (1+10+(c-'a'));
+	return o-1;
+}
 
 int
 dec16(uchar *out, int lim, char *in, int n)
@@ -10,14 +32,8 @@ dec16(uchar *out, int lim, char *in, int n)
 	uchar *eout = out + lim;
 
 	while(n-- > 0){
-		c = *in++;
-		if('0' <= c && c <= '9')
-			c = c - '0';
-		else if('a' <= c && c <= 'z')
-			c = c - 'a' + 10;
-		else if('A' <= c && c <= 'Z')
-			c = c - 'A' + 10;
-		else
+		c = dec16chr(*in++);
+		if(c < 0)
 			continue;
 		w = (w<<4) + c;
 		i++;
@@ -44,8 +60,8 @@ enc16(char *out, int lim, uchar *in, int n)
 		c = *in++;
 		if(out + 2 >= eout)
 			goto exhausted;
-		*out++ = t16e[c>>4];
-		*out++ = t16e[c&0xf];
+		*out++ = enc16chr(c>>4);
+		*out++ = enc16chr(c&15);
 	}
 exhausted:
 	*out = 0;
diff --git a/sys/src/libc/port/u32.c b/sys/src/libc/port/u32.c
index 7423984a2..9ad9eb781 100644
--- a/sys/src/libc/port/u32.c
+++ b/sys/src/libc/port/u32.c
@@ -1,21 +1,44 @@
 #include <u.h>
 #include <libc.h>
 
+#define between(x,min,max)	(((min-1-x) & (x-max-1))>>8)
+
+int
+enc32chr(int o)
+{
+	int c;
+
+	c  = between(o,  0, 25) & ('A'+o);
+	c |= between(o, 26, 31) & ('2'+(o-26));
+	return c;
+}
+
+int
+dec32chr(int c)
+{
+	int o;
+
+	o  = between(c, 'A', 'Z') & (1+(c-'A'));
+	o |= between(c, 'a', 'z') & (1+(c-'a'));
+	o |= between(c, '2', '7') & (1+26+(c-'2'));
+	return o-1;
+}
+
 int
 dec32(uchar *dest, int ndest, char *src, int nsrc)
 {
-	char *s, *tab;
 	uchar *start;
-	int i, u[8];
+	int i, j, u[8];
 
 	if(ndest+1 < (5*nsrc+7)/8)
 		return -1;
 	start = dest;
-	tab = "23456789abcdefghijkmnpqrstuvwxyz";
 	while(nsrc>=8){
 		for(i=0; i<8; i++){
-			s = strchr(tab,(int)src[i]);
-			u[i] = s ? s-tab : 0;
+			j = dec32chr(src[i]);
+			if(j < 0)
+				j = 0;
+			u[i] = j;
 		}
 		*dest++ = (u[0]<<3) | (0x7 & (u[1]>>2));
 		*dest++ = ((0x3 & u[1])<<6) | (u[2]<<1) | (0x1 & (u[3]>>4));
@@ -29,8 +52,10 @@ dec32(uchar *dest, int ndest, char *src, int nsrc)
 		if(nsrc == 1 || nsrc == 3 || nsrc == 6)
 			return -1;
 		for(i=0; i<nsrc; i++){
-			s = strchr(tab,(int)src[i]);
-			u[i] = s ? s-tab : 0;
+			j = dec32chr(src[i]);
+			if(j < 0)
+				j = 0;
+			u[i] = j;
 		}
 		*dest++ = (u[0]<<3) | (0x7 & (u[1]>>2));
 		if(nsrc == 2)
@@ -50,60 +75,57 @@ out:
 int
 enc32(char *dest, int ndest, uchar *src, int nsrc)
 {
-	char *tab, *start;
+	char *start;
 	int j;
 
-	if(ndest <= (8*nsrc+4)/5 )
+	if(ndest <= (8*nsrc+4)/5)
 		return -1;
 	start = dest;
-	tab = "23456789abcdefghijkmnpqrstuvwxyz";
 	while(nsrc>=5){
 		j = (0x1f & (src[0]>>3));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1c & (src[0]<<2)) | (0x03 & (src[1]>>6));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1f & (src[1]>>1));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x10 & (src[1]<<4)) | (0x0f & (src[2]>>4));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1e & (src[2]<<1)) | (0x01 & (src[3]>>7));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1f & (src[3]>>2));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x18 & (src[3]<<3)) | (0x07 & (src[4]>>5));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1f & (src[4]));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		src  += 5;
 		nsrc -= 5;
 	}
 	if(nsrc){
 		j = (0x1f & (src[0]>>3));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1c & (src[0]<<2));
 		if(nsrc == 1)
 			goto out;
 		j |= (0x03 & (src[1]>>6));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1f & (src[1]>>1));
-		if(nsrc == 2)
-			goto out;
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x10 & (src[1]<<4));
-		if(nsrc == 3)
+		if(nsrc == 2)
 			goto out;
 		j |= (0x0f & (src[2]>>4));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1e & (src[2]<<1));
-		if(nsrc == 4)
+		if(nsrc == 3)
 			goto out;
 		j |= (0x01 & (src[3]>>7));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x1f & (src[3]>>2));
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 		j = (0x18 & (src[3]<<3));
 out:
-		*dest++ = tab[j];
+		*dest++ = enc32chr(j);
 	}
 	*dest = 0;
 	return dest-start;
diff --git a/sys/src/libc/port/u64.c b/sys/src/libc/port/u64.c
index 432cec899..44f716fbe 100644
--- a/sys/src/libc/port/u64.c
+++ b/sys/src/libc/port/u64.c
@@ -1,29 +1,33 @@
 #include <u.h>
 #include <libc.h>
 
-enum {
-	INVAL=	255
-};
+#define between(x,min,max)	(((min-1-x) & (x-max-1))>>8)
 
-static uchar t64d[256] = {
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,   62,INVAL,INVAL,INVAL,   63,
-      52,   53,   54,   55,   56,   57,   58,   59,   60,   61,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,    0,    1,    2,    3,    4,    5,    6,    7,    8,    9,   10,   11,   12,   13,   14,
-      15,   16,   17,   18,   19,   20,   21,   22,   23,   24,   25,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,   26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40,
-      41,   42,   43,   44,   45,   46,   47,   48,   49,   50,   51,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
-   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL
-};
-static char t64e[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+int
+enc64chr(int o)
+{
+	int c;
+
+	c  = between(o,  0, 25) & ('A'+o);
+	c |= between(o, 26, 51) & ('a'+(o-26));
+	c |= between(o, 52, 61) & ('0'+(o-52));
+	c |= between(o, 62, 62) & ('+');
+	c |= between(o, 63, 63) & ('/');
+	return c;
+}
+
+int
+dec64chr(int c)
+{
+	int o;
+
+	o  = between(c, 'A', 'Z') & (1+(c-'A'));
+	o |= between(c, 'a', 'z') & (1+26+(c-'a'));
+	o |= between(c, '0', '9') & (1+52+(c-'0'));
+	o |= between(c, '+', '+') & (1+62);
+	o |= between(c, '/', '/') & (1+63);
+	return o-1;
+}
 
 int
 dec64(uchar *out, int lim, char *in, int n)
@@ -36,9 +40,8 @@ dec64(uchar *out, int lim, char *in, int n)
 	b24 = 0;
 	i = 0;
 	while(n-- > 0){
-
-		c = t64d[*(uchar*)in++];
-		if(c == INVAL)
+		c = dec64chr(*in++);
+		if(c < 0)
 			continue;
 		switch(i){
 		case 0:
@@ -58,8 +61,8 @@ dec64(uchar *out, int lim, char *in, int n)
 			*out++ = b24>>16;
 			*out++ = b24>>8;
 			*out++ = b24;
-			i = -1;
-			break;
+			i = 0;
+			continue;
 		}
 		i++;
 	}
@@ -89,34 +92,34 @@ enc64(char *out, int lim, uchar *in, int n)
 	char *e = out + lim;
 
 	for(i = n/3; i > 0; i--){
-		b24 = (*in++)<<16;
-		b24 |= (*in++)<<8;
+		b24 = *in++<<16;
+		b24 |= *in++<<8;
 		b24 |= *in++;
 		if(out + 4 >= e)
 			goto exhausted;
-		*out++ = t64e[(b24>>18)];
-		*out++ = t64e[(b24>>12)&0x3f];
-		*out++ = t64e[(b24>>6)&0x3f];
-		*out++ = t64e[(b24)&0x3f];
+		*out++ = enc64chr(b24>>18);
+		*out++ = enc64chr((b24>>12)&0x3f);
+		*out++ = enc64chr((b24>>6)&0x3f);
+		*out++ = enc64chr(b24&0x3f);
 	}
 
 	switch(n%3){
 	case 2:
-		b24 = (*in++)<<16;
-		b24 |= (*in)<<8;
+		b24 = *in++<<16;
+		b24 |= *in<<8;
 		if(out + 4 >= e)
 			goto exhausted;
-		*out++ = t64e[(b24>>18)];
-		*out++ = t64e[(b24>>12)&0x3f];
-		*out++ = t64e[(b24>>6)&0x3f];
+		*out++ = enc64chr(b24>>18);
+		*out++ = enc64chr((b24>>12)&0x3f);
+		*out++ = enc64chr((b24>>6)&0x3f);
 		*out++ = '=';
 		break;
 	case 1:
-		b24 = (*in)<<16;
+		b24 = *in<<16;
 		if(out + 4 >= e)
 			goto exhausted;
-		*out++ = t64e[(b24>>18)];
-		*out++ = t64e[(b24>>12)&0x3f];
+		*out++ = enc64chr(b24>>18);
+		*out++ = enc64chr((b24>>12)&0x3f);
 		*out++ = '=';
 		*out++ = '=';
 		break;