How can you determine if an LM hash you extracted contains a password that is less than 8 characters long?

Although hashes are one-way functions that cannot be reversed directly, the structural property of LM hashing does expose password length information through the constant right-side value.

LM hashing pads each 7-character password chunk with null bytes before performing DES encryption independently on each half. When a password is less than 8 characters long, the second 7-character chunk is entirely null bytes, which always encrypts to the well-known constant value 'AAD3B435B51404EE', making the right portion of the 32-character LM hash a reliable indicator that the password is 7 characters or fewer.

LM hashes do not start with a fixed prefix like 'AB923D'; this is a fabricated value with no basis in the DES-based LM hashing algorithm.

The left portion of the LM hash reflects the encryption of the first 7 characters and varies based on what those characters are, so it is not a constant indicator.

The right portion does not appear as all zeros; it produces the specific constant DES ciphertext 'AAD3B435B51404EE', which is a non-zero recognizable pattern.