Re: Newbie question about AES encryption

On 30 Oct 2006 16:47:39 -0800, Mark <mminnie@xxxxxxxxxxxxxx> wrote:
I download some free code to create SHA1 hashes and AES encryption.
Using this code I created a program to encrypt strings by first
initializing the cipher with a SHA1 hash of the password, and then
encrypting the data with the password. It seems to work great by
encrypting a string such as "Encrypted String" and a password of
"password" to a resulting string of "J4lgK+NgpWWtXTyWmeNgow==". Now if
I try and decrypt ONLY PART of the encrypted string, say
"J4lgK+NgpWWtXT" with the password "password", part of the string is
decrypted successfully. I get a decrypted result of "Encrypted". This
seems odd. I would think by truncating part of the decrypted string, I
would get a bunch of garbage in the decrypted string.

Is this a cause for concern?

1. Remember that secrecy and authentication are independent
aspects of cryptography. Were you hoping for authentication?

2. You'd probably profit from a look at Wikipedia's article
on block cipher modes of operation:
http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation

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