1 // Copyright 2012 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef CRYPTO_SECURE_UTIL_H_ 6 #define CRYPTO_SECURE_UTIL_H_ 7 8 #include <stddef.h> 9 10 #include "base/containers/span.h" 11 #include "crypto/crypto_export.h" 12 13 namespace crypto { 14 15 // Performs a constant-time comparison of two strings, returning true if the 16 // strings are equal. Note that while the contents of the strings are not 17 // leaked, their *lengths* may be leaked - there is no way to do a comparison 18 // whose timing does not depend, at least coarsely, on the length of the data 19 // being compared. 20 // 21 // For cryptographic operations, comparison functions such as memcmp() may 22 // expose side-channel information about input, allowing an attacker to 23 // perform timing analysis to determine what the expected bits should be. In 24 // order to avoid such attacks, the comparison must execute in constant time, 25 // so as to not to reveal to the attacker where the difference(s) are. 26 // For an example attack, see 27 // http://groups.google.com/group/keyczar-discuss/browse_thread/thread/5571eca0948b2a13 28 CRYPTO_EXPORT bool SecureMemEqual(base::span<const uint8_t> s1, 29 base::span<const uint8_t> s2); 30 31 } // namespace crypto 32 33 #endif // CRYPTO_SECURE_UTIL_H_ 34 35