Nagram/TMessagesProj/jni/voip/webrtc/base/hash

Choosing A Hash Function

Note: this document is still very much a work-in-progress. Currently missing:

• recommendations for hashed containers
• recommendations for a better persistent hash
• recommendations for a secure hash

If a hash function with unchanging output is needed, please select from one of the unchanging forever options below.

Non-cryptographic

name	input	output	unchanging forever	notes
Hash()	overloaded	uint32_t	no	This function is currently being updated to return size_t.
PersistentHash()	overloaded	uint32_t	yes	Fairly weak but widely used for persisted hashes.
CityHash64()	base::span<const uint8_t>	uint64_t	yes (note 1)	Version 1.0.3. Has some known weaknesses.
CityHash64WithSeed()	base::span<const uint8_t>	uint64_t	yes (note 1)	Version 1.0.3. Has some known weaknesses.

Cryptographic

There are no hashes in //base that provide cryptographic security.

name	input	output	unchanging forever	notes
MD5String()	std::string	std::string	yes	INSECURE
SHA1HashString	std::string	std::string	yes	INSECURE

Deprecated

Note: CRC32, Murmur2, and Murmur3 will be listed here.

Note 1: While CityHash is not guaranteed unchanging forever, the version used in Chrome is pinned to version 1.0.3.