I have really googled the entire internet but could not find a clear algorithm for hummingbird-1 cryptography.The problem emerges in the decryption module:
- What is the initial value of state register $RS_1$, $RS_2$, $RS_3$, $RS_4$.
- What is the initial value of LFSR?
- Having known the encryption block cipher $Ek_1$, $Ek_2$, $Ek_3$, $Ek_4$,how can we get to $Dk_1$, $Dk_2$, $Dk_3$, $Dk_4$?
Here is a link to the Encryption and Decryption Structure: Encryption and Decryption Structure