83Plus:BCALLs:80C0

Synopsis

Official Name: bignumpowermod17

BCALL Address: 80C0

Raises a big integer to the 17th power.

Inputs

• 8182 holds the signature
• 8000 holds the modulus, another big integer

Outputs

• OP1-OP6 hold the plaintext, a big integer
• DE points to OP1

Destroys

• All registers
• 8100h: 130-byte area which the multiplication routine uses to store its result
• 8182h: 65-byte area used as the first argument to the multiplication routine
• 81C3h: 65-byte area used as the second argument to the multiplication routine

Comments

This BCALL takes a large integer pointed at address 8182h and raises it to the 17th power (modulo the current public key.) The OS uses this to decrypt RSA signatures, such as those used for certificate blocks. This differs only from RSAValidate in that this romcall expects the signature to already be copied to 8182h.