How does ARJ Password Recovery work?

ARJ password recovery options vary depending upon which version of ARJ was used to create the archive. Early version of ARJ utilized a simple XOR encryption scheme. Because the password is used to generate the encryption key, the difficulty of decrypting an ARJ archive depends directly on the length of the password which was used to encrypt the archive.

For more information on ARJ's XOR encryption, read Method of attacking arj encrypted files

More recent versions of ARJ utilize a version of the Gost algorithm for strong encryption.

ARJ XOR encryption is vulnerable to a known plaintext attack, but this requires that you have an unencrypted version of at least one file in the encrypted archive.

It is also possible to accomplish dictionary attacks and brute force attacks on ARJ archives.