| # 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()`][hash] | overloaded | `uint32_t` | no | This function is currently being updated to return `size_t`. |
| [`PersistentHash()`][persistenthash] | overloaded | `uint32_t` | yes | Fairly weak but widely used for persisted hashes. |
| [`CityHash64()`][cityhash64] | `base::span<const uint8_t>` | `uint64_t` | yes (note 1) | Version 1.0.3. Has some known weaknesses. |
| [`CityHash64WithSeed()`][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()`][md5string] | `std::string` | `std::string` | yes | **INSECURE** |
| [`SHA1HashString`][sha1string] | `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. |
| |
| [hash]: https://cs.chromium.org/chromium/src/base/hash/hash.h?l=26 |
| [persistenthash]: https://cs.chromium.org/chromium/src/base/hash/hash.h?l=36 |
| [cityhash64]: https://cs.chromium.org/chromium/src/base/hash/city_v103.h?l=19 |
| [cityhash64withseed]: https://cs.chromium.org/chromium/src/base/hash/city_v103.h?l=20 |
| [md5string]: https://cs.chromium.org/chromium/src/base/hash/md5.h?l=74 |
| [sha1string]: https://cs.chromium.org/chromium/src/base/hash/sha1.h?l=22 |
