troubles with crypto ...

took me a long time to complete my cryptographic applications chapter. didn't do well for the test, especially the part involving public private keys and the size of the message digest produced by different hashing algorithms.

found an extract from a textbook which helped a lot with the public private key issue.
'if you want to encrypt a message, use the sender's public key.
if you want to decrypt a message sent to you, use your private key.
if you want to digitally sign a message you are sending to someone else, use your own private key.
if you want to verify the signature on a message sent by someone else, use the sender's public key.'
hope these tips will help those having the same difficulty as i am.

for the size of the message digest from different hashing algorithms, i have not found any simple rules to follow. think there is not much choice but to memorize the facts. SHA-1 generates 160 bits digest 80 bits protection, SHA-256 generates 256 bits 128 bits protection, SHA-512 generates 512 bits 256 bits protection. MD2 generates 128 bits digests (including 16 bit appended checksum), MD5 generates .... i'm boring myself silly with the memorization.

moving to a more interesting piece of news, Dell will be recalling 4.1m notebook batteries manufactured by Sony between Apr 2004 and Jul 2006 in response to the six overheating incidents that caused property damages. i wonder how this will hurt Dell, having been involved with exploding notebooks this year. some analysts, however think that this move will buy goodwill from customers and potential customers. guess i know too little about how the coporate world works to figure it out on my own.