Made Base64 decoding constant-time (with regards to actual data byte contents).

[BearSSL] / src / codec / pemdec.t0

diff --git a/src/codec/pemdec.t0 b/src/codec/pemdec.t0
index 4ebf0dd..2237abb 100644 (file)
--- a/src/codec/pemdec.t0
+++ b/src/codec/pemdec.t0
@@ -170,13 +170,21 @@ cc: read8-native ( -- x ) {
 
 \ Convert a Base64 character to its numerical value. Returned value is
 \ 0 to 63 for Base64 characters, -1 for '=', and -2 for all other characters.
-: from-base64 ( char -- x )
-       dup dup `A >= swap `Z <= and if 65 - ret then
-       dup dup `a >= swap `z <= and if 71 - ret then
-       dup dup `0 >= swap `9 <= and if 4 + ret then
-       dup `+ = if drop 62 ret then
-       dup `/ = if drop 63 ret then
-       `= <> 1- ;
+cc: from-base64 ( char -- x ) {
+       uint32_t c = T0_POP();
+       uint32_t p, q, r, z;
+       p = c - 0x41;
+       q = c - 0x61;
+       r = c - 0x30;
+
+       z = ((p + 2) & -LT(p, 26))
+               | ((q + 28) & -LT(q, 26))
+               | ((r + 54) & -LT(r, 10))
+               | (64 & -EQ(c, 0x2B))
+               | (65 & -EQ(c, 0x2F))
+               | EQ(c, 0x3D);
+       T0_PUSHi((int32_t)z - 2);
+}
 
 \ Test whether a character is whitespace (but not a newline).
 : ws? ( x -- bool )