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The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, [3] and was specified in 1992 as RFC 1321. MD5 can be used as a checksum to verify data integrity against unintentional corruption.
The MD5 hash of the combined username, authentication realm and password is calculated. The result is referred to as HA1. The MD5 hash of the combined method and digest URI is calculated, e.g. of "GET" and "/dir/index.html". The result is referred to as HA2.
Programs for breaking crypt(1) encryption are widely available. Bob Baldwin's public domain Crypt Breaker's Workbench, which was written in 1984-1985, is an interactive tool that provides successive plaintext guesses that must be corrected by the user. It also provides a working crypt(1) implementation used by modern BSD distributions. [6]
Hashcat is a password recovery tool. It had a proprietary code base until 2015, but was then released as open source software. Versions are available for Linux, macOS, and Windows. Examples of hashcat-supported hashing algorithms are LM hashes, MD4, MD5, SHA-family and Unix Crypt formats as well as algorithms used in MySQL and Cisco PIX.
For instance, MD5-Crypt uses a 1000 iteration loop that repeatedly feeds the salt, password, and current intermediate hash value back into the underlying MD5 hash function. [4] The user's password hash is the concatenation of the salt value (which is not secret) and the final hash.
MD5 itself would provide good cryptographic strength for the password hash, but it is designed to be quite quick to calculate relative to the strength it provides. The crypt() scheme is designed to be expensive to calculate, to slow down dictionary attacks. The printable form of MD5 password hashes starts with $1$.
This attack is normally harder, a hash of n bits can be broken in 2 (n/2)+1 time steps, but is much more powerful than a classical collision attack. Mathematically stated, given two different prefixes p 1, p 2, the attack finds two suffixes s 1 and s 2 such that hash(p 1 ∥ s 1) = hash(p 2 ∥ s 2) (where ∥ is the concatenation operation).
This follows the Modular Crypt Format [12] format used when storing passwords in the OpenBSD password file: $1$ : MD5-based crypt ('md5crypt') $2$ : Blowfish-based crypt ('bcrypt')