Hello, > is it possible to change the OpenSSL RSA functions so that I can use > a different - may be a variable - block size. At the moment the block > size on the OpenSSL RSA functions depends on the length of the RSA > key pair and the kind of padding (following PKCS#1 v1.5, which means > 11 byte random data): > > key lenght block size available space > > 2024 bit 256 byte 245 byte > 1024 bit 128 byte 105 byte > 768 bit 96 byte 85 > > Normally, on symmetric encryption the block size _must_ be the same > as the key lenght. Not exactly, for example: AES128: key: 16bytes, block: 16bytes AES192: key: 24bytes, block: 16bytes AES256: key: 32bytes, block: 16bytes DES3 : key: 24bytes, block: 8bytes and of course des which has key_len == block_len: DES : key: 8bytes, block: 8bytes
> But on asymmetric encryption methods - I think - > the block size not depends on that restriction, or is there another > point, which forces such a fixed block size? Amount of data which may be encrypted with RSA depends on algorithm. If you have private key (d,n) and public key (e,n) where n=p*q, where p and q are prime numbers. Encryption of plain P: C = P^e mod n Decryption of cipher C: P = C^d mod n As you see, you get always result as number from 0 to n-1 (modulo operation) and n is RSA key size. To be more specific, RSA operation is performed inside multiplicative group. Best regards, -- Marek Marcola <[EMAIL PROTECTED]> ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager [EMAIL PROTECTED]
