# What is the exact algorithm for encryption and decryption with hummingbird-1 cryptography?

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:

1. What is the initial value of state register $$RS_1$$, $$RS_2$$, $$RS_3$$, $$RS_4$$.
2. What is the initial value of LFSR?
3. 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