Reused key attack.
Fencry uses a 256 bits key (secret) and an open 256 Bits random key to
encrypt the text.
The open random key are mixed with the secret key.
making a new secret key.
This makes every cipher text unique, even if the same secret cipher key
is reused.
The open key (labeld as green) are included in the beginning of the
cipher text (yellow).
Before decoding the open key is extracted from the cipher and mixed with
the secret key
After key mixing, the sub keys are made (key scheduling) and the cipher
is decrypted.
The use of a random open key in a stream cipher helps protecting against
the most
common attack against stream ciphers, "Reused key attack". Read
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