How to add seek and position capabilities to CryptoStream

Question

I was trying to use CryptoStream with AWS .NET SDk it failed as seek is not supported on CryptoStream. I read somewhere with content length known we should be able to add th

Answer 1

As an extension to Mark Gravell's answer, the seekability of a cipher depends on the Mode Of Operation you're using for the cipher. Most modes of operation aren't seekable, because each block of ciphertext depends in some way on the previous one. ECB is seekable, but it's almost universally a bad idea to use it. CTR mode is another one that can be accessed randomly, as is CBC.

All of these modes have their own vulnerabilities, however, so you should read carefully and think long and hard (and preferably consult an expert) before choosing one.