chris holt wrote: > > I do not have in depth knowledge about the cryptography schemes and don't > under stand why I would be getting this error when encrypting a file with > RSA. > > RSA/OAEP-MGF1(SHA-1): message too long for this public key > > How does the message length correspond to the public key? > Any help would be appreciated? >
Although RSA can be used in its raw format to encrypt a whole file it's not recommended and it's very risky; there are many reasons you should use some cooked version (like OAEP-MGF1(SHA-1)) which are specifically designed to encrypt only a small portion of a message, typically a session key, in a secure manner. This message has to be a fraction of the public key length (say 1/2 or 1/3, I do not have the PKCS spec. here right now, but these numbers seems to be quite adequate for a session key). You can then use the session key and a symmetric cipher (for example cast, blowfish, 3des, rijndael, ecc.) to encrypt whatever you want. At destination, the receiver recovers the session key using RSA and its private key, then uses the symmetric cipher to decrypt the payload. With minimal work, you should be able to pack everything in one encrypted file. Bye, -- Giuliano Bertoletti e-Security Manager Intrinsic - Security Monitoring http://www.intrinsic.it COOL-FIRE: la soluzione Firewall per Windows NT/2000 http://www.symbolic.it/Prodotti/cool-fire.html SYMBOLIC S.p.A. Tel: +39 0521 776180 / Fax: +39 0521 776190
