1. How is the IV handled in (AES) encryption? --Actually, in AES in CBC mode, the ciphertext is dependent on the already computed ciphertext block. That is, CT for block k is dependent on CT of block k-1 and plain text for block k. (How it is dependent is a complex maths). But how do you know the ciphertext for 1st block? This is where IV comes in.
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of David Irvine Sent: Thursday, August 17, 2006 5:27 PM To: openssl-users@openssl.org Subject: General Questions Hi This may be a double post if it is I apologise (I think I may have posted this before I was authorised by majordomo). I have started using encryption and thought I would try this out. My question(s) are as follows - please be gentle 1: How is the IV handled in (AES) encryption - I can see supplying an initial vector is good but it also appears this should change with every encryption (if you like). So does a user have to know this + key ? 2: Is it possible to alter a key size say I am using SHA256 and want to output a SHA256 hash of a users password to use as a key ? Also can I pass something to openssl to get a hex digest ? 3: If a cracker can only retrieve 1 part of an encrypted file that has been deliberately split up - would having this 'part file' help or hinder the task of decrypting the contents of that file. 4: Is there a way that when attempting to decrypt a file you cannot know if you have been successful, i.e. you don't know the contents and try a key - you get an output from the attempt but it is not obvious if that output is correct (i.e file encrypted multiple times) or do all the encryption algorithms give a pass or fail or empty output. (i.e I tell you my pass-phrase is X and you use this to get output Y but you don't know what output Y is [could be further encryption], can you tell just be running the decryption algorithm that the key was a valid key?) I know this is a bit much for a first question but I am researching a lot and it is fairly new (but hopefully I am a quick learner). David DISCLAIMER ========== This e-mail may contain privileged and confidential information which is the property of Persistent Systems Pvt. Ltd. It is intended only for the use of the individual or entity to which it is addressed. If you are not the intended recipient, you are not authorized to read, retain, copy, print, distribute or use this message. If you have received this communication in error, please notify the sender and delete all copies of this message. Persistent Systems Pvt. Ltd. does not accept any liability for virus infected mails. ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager [EMAIL PROTECTED]
