Technical information on ASIC mining

[hasyu]

Hi everyone,

even if the search for online info has been long, I have not found the answers to the questions I have about ASIC mining, so I have to ask you!

1) Is it correct to say that the cryptographic base used by ASICs is the digital signature?
2) Does this mean that encryption is asymmetric?
3) Is the underlying algorithm SHA256 or ECDSA? I also read double SHA256... I think I've gone a little confused