83Plus:BCALLs:801B

Synopsis

Official Name: RSAValidate

BCALL Address: 801B

Raises a big integer to the 17th power.

Inputs

• HL points to the signature, a big integer
• 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 to by HL 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.