Magic hashes – PHP hash "collisions"
Register with password 1 and then sign in with password 2. If you're in then the storage uses specified algorithm to hash the password and PHP uses
== to compare them (for MD5, SHA-1, and plaintext).
For MD5, SHA-1 and SHA-2 family, it uses the long-known trick (it actually is a documented feature, see PHP type comparison tables & Floating point numbers) that for PHP
'0e1' == '00e2' == '0', it just uses it for practical purposes. Any password matches any other password from the list. This is a different trick than integral strings overflowing into floating point numbers, just spot the difference between these two lines.
These are all the algorithms with magic hashes:
To quote @0xb0bb, "there are other applications for magic hashes other than password comparisons (such as caching layers or data derived from the output of a hash function) where these known insecure, lesser known and pseudo-hash algorithms can be found more readily."
For plaintext, it uses various conversion tricks. First password will match just the second one. Tricks are grouped by PHP versions allowing them.
bcrypt truncates passwords to a maximum length of 72 characters. The passwords match if the first 72 characters of both passwords match.
descrypt (traditional UNIX DES crypt) truncates passwords to a maximum length of 8 characters. The passwords also match if the first 8 characters of both passwords match, see the "General cross-check" section.
If you use a password longer than 64 bytes and hash it with PBKDF2-HMAC-SHA1, it is first pre-hashed with SHA1, so
PBKDF2-HMAC-SHA1(password1) === PBKDF2-HMAC-SHA1(password2) because
sha1(password1) === bin2hex(password2). The similar pre-hashing is applied in case of PBKDF2-HMAC-SHA224 and PBKDF2-HMAC-SHA256.
Right now there's just one magic hash in each thanks to Norbert Tihanyi, more will be hopefully added in the future.
- MD5: Tweet, code, contributions by roycewilliams, Norbert Tihanyi, ethernetlord, 0xb0bb, myst404
- SHA-1: Tweet, code, contributions by roycewilliams, 0xb0bb, matlink, myst404
- Plaintext: Tweet, code
- bcrypt: code
- PBKDF2-HMAC-SHA1 by Christian "CodesInChaos" Winnerlein, as explained by Mathias Bynens, code
- PBKDF2-HMAC-SHA224 by Norbert Tihanyi, code
- PBKDF2-HMAC-SHA256 by Jens 'atom' Steube, code
- Tiger/192,3 by Norbert Tihanyi
- SHA-224 by Norbert Tihanyi, hops, 0xb0bb, myst404
- SHA-256 by Norbert Tihanyi, Chick3nman, roycewilliams, matlink
- CRC32, CRC32b, FNV-1a/32, FNV-1a/64, FNV-1/32, FNV-1/64, HAVAL-128,3, HAVAL-128,4, HAVAL-128,5, HAVAL-160,3, HAVAL-160,4, HAVAL-160,5, JOAAT, MD2, MD4, RIPEMD-128, RIPEMD-160, Tiger/128,3, Tiger/128,4, Tiger/160,3, Tiger/160,4 by 0xb0bb
- descrypt by James M. Hall, hops
How to calculate your own
I've used my laptop, few
foreach?) loops, many CPU cycles and an external fan back in 2014 but today you can/should use a GPU and a modified hashcat for that. See this write-up by Carl Löndahl and 0xb0bb.
Chick3nman & co. is also working on their version of hashcat, stay tuned.