Identifying Cryptographic Hash Types by Sight

original source: pete on software com

Hash lengths:

• MD5: 32 hexadecimal characters (128 bits).
• SHA-1: 40 hexadecimal characters (160 bits).
• SHA-256: 64 hexadecimal characters (256 bits).
• SHA-512: 128 hexadecimal characters (512 bits).
• bcrypt: Typically around 60 characters (includes a salt).

Formatting Signature

bcrypt hashes often start with $2a$, $2b$, or $2y$.

In a Linux /etc/shadow passwd file the prefix format is: $id$salt$hashed

• $1$ is MD5
• $2a$ is Blowfish
• $2y$ is Blowfish
• $5$ is SHA-256
• $6$ is SHA-512
• $y$ is yescrypt

NOTE: Bcrypt is a password-hashing function based on the Blowfish cipher, designed to securely store passwords by incorporating salting and a computationally intensive process to resist brute-force attacks. While Blowfish is a general-purpose encryption algorithm, bcrypt specifically focuses on password security.

• MD5 is typically a straightforward 32-character hexadecimal string.
• NTLM (used in Windows environments) often has a 32-character hexadecimal format similar to MD5 but with a central colon : is distinct in purpose. They are susciptable to rainbow table bruteforcing with a tool like ophcrack.

Context

Password Databases: If you’re analyzing a password database, it’s common to find hashes like bcrypt, PBKDF2, or even older ones like MD5. File Integrity Checks: If the hash is related to file integrity checks (e.g., software downloads), SHA-256 or SHA-512 is often used. Certificates and Signatures: Digital certificates or signatures may use SHA-256 or SHA-1, although SHA-1 has been largely deprecated.

Distinctive markers at specific points in the hash.

Some hash functions, particularly those used for passwords (like bcrypt, PBKDF2, and Argon2) employ salting and iterations to increase security. The salt is a random value added to the input to ensure identical passwords don’t produce identical hashes. Hashes with salts often have longer lengths and may include markers or delimiters in the format, like the way you might find a Bcrypt hash that starts with $2a$10$… where 10 is the cost factor, meaning it hashed and rehashed ten times.

For a hash like $2y$12$EXRkfkdmXn2gzds2SSituJWMqp3hPFO4lH/vqFhD8aJL.lfwBby4a from a penetration test and the $2y$ indicates algorithm is bcrypt and 12 indicates the number of iterations (also called the cost factor). You can then use a tool like John the Ripper or Hashcat with your favorite wordlists, specifying bcrypt as the algorithm.

Python’s bcrypt module provides methods for hashing and checking passwords:

>>> import bcrypt

>>> bcrypt.hashpw("PASSWD".encode('utf-8'), bcrypt.gensalt(4)).decode('utf-8')
'$2b$04$4aUdoXc5aPXQBkWGpHZiS.OhmMOMqTEUp7O9FV.RGrQRCClpHypcS'

>>> bcrypt.hashpw("PASSWD".encode('utf-8'), bcrypt.gensalt(15)).decode('utf-8')
'$2b$15$tTGjZ5RztX4neMM8y0.vu.YsuJ8/BCnEYGOG07INUZRXlZEtOOVkK'