1 // Copyright 2015-2016 Brian Smith.
2 //
3 // Permission to use, copy, modify, and/or distribute this software for any
4 // purpose with or without fee is hereby granted, provided that the above
5 // copyright notice and this permission notice appear in all copies.
6 //
7 // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
8 // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
10 // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14
15 //! Constant-time operations.
16
17 use crate::{c, error};
18
19 /// Returns `Ok(())` if `a == b` and `Err(error::Unspecified)` otherwise.
20 /// The comparison of `a` and `b` is done in constant time with respect to the
21 /// contents of each, but NOT in constant time with respect to the lengths of
22 /// `a` and `b`.
verify_slices_are_equal(a: &[u8], b: &[u8]) -> Result<(), error::Unspecified>23 pub fn verify_slices_are_equal(a: &[u8], b: &[u8]) -> Result<(), error::Unspecified> {
24 if a.len() != b.len() {
25 return Err(error::Unspecified);
26 }
27 let result = unsafe { GFp_memcmp(a.as_ptr(), b.as_ptr(), a.len()) };
28 match result {
29 0 => Ok(()),
30 _ => Err(error::Unspecified),
31 }
32 }
33
34 extern "C" {
GFp_memcmp(a: *const u8, b: *const u8, len: c::size_t) -> c::int35 fn GFp_memcmp(a: *const u8, b: *const u8, len: c::size_t) -> c::int;
36 }
37
38 #[cfg(test)]
39 mod tests {
40 use crate::{bssl, error};
41
42 #[test]
test_constant_time() -> Result<(), error::Unspecified>43 fn test_constant_time() -> Result<(), error::Unspecified> {
44 extern "C" {
45 fn bssl_constant_time_test_main() -> bssl::Result;
46 }
47 Result::from(unsafe { bssl_constant_time_test_main() })
48 }
49 }
50