AES-256-CFB cuts off message when using `random_iv` - ruby

Question

I have two scripts for encrypting and decrypting messages using AES.
Here's encrypt.rb:
require 'openssl'
require 'base64'
require 'digest'
KEY = 'sekrit_key'
MESSAGE = "My Name is Rabbit and I don't know anything!"
cipher = OpenSSL::Cipher::AES256.new(:CFB)
cipher.encrypt
cipher.key = KEY
# hexdigest the IV to make sure encode64 doesn't fuck up
iv = Digest::MD5.hexdigest(cipher.random_iv)
cipher.iv = iv
encrypted = cipher.update(secret_message)+cipher.final
puts Base64.urlsafe_encode64(iv+'|'+encrypted.encode)
... and decrypt.rb:
require 'openssl'
require 'base64'
KEY = 'sekrit_key'
encrypted_message = STDIN.read.strip
parts = Base64.urlsafe_decode64(encrypted_message ).split('|')
iv = parts[0]
encrypted = parts[1]
decipher = OpenSSL::Cipher::AES256.new(:CFB)
decipher.decrypt
decipher.key = KEY
decipher.iv = iv
message = decipher.update(encrypted)+decipher.final
if message.eql?("My Name is Rabbit and I don't know anything!")
print '.'
else
puts
puts encrypted_message
puts message
end
When I now continuosly run both scripts, My output is cut off quite often!
$ while true; do ruby encrypt.rb | ruby decrypt.rb; done
....
YmZhNDg2ODJjNGZiOGIzZTcyMzAwYzMxZWUwNWI0Y2V8w2aJk930EL3gh3rfQsd2B3xZKy5wjoCzlZoYHBgmv6m51ZwAWQHGtCJoNRg=
My Name is Rabbi
..
YjMwNDQxOGRjMjg4NGEzOThmM2IwNGFiZDBiZTQxZGZ8OfLyjGQGKV3PPUpCvfL08IDuk7M7d3w7fj6F5Rql94jkRdwaCuuMfedqtFk=
My Name is Rabbit and
..
OWUxYzFlZWU5MTc4NGZjYWYxYzZiOGEwOTBjOGMxYzJ8g7I4X_Dt6K9ufByMhLBGlpoYCv8vlR0lTBqP-zS647tmmFh81rXdR8T-UkM=
My Name i
....
# and so on
Why are so many of my messages cut off?
Update: When using a fixed IV in encrypt.rb (eg. substitute cipher.random_iv with KEY) instead of a randomly generated, the problem does not occur.

Answer 1

The problem stems from the fact that you're treating binary data as strings. iv as well as encrypted.encode are binary and you're concatenating them with "|" (a string). Both iv as well as the message may contain the pipe character which will cause problems when splitting. In general, it's best to base64 both parts separately.
Here's working code:
encrypt.rb
require 'openssl'
require 'base64'
require 'digest'
KEY = 'sekrit_key123456' * 2
MESSAGE = "My Name is Rabbit and I don't know anything!"
cipher = OpenSSL::Cipher::AES256.new(:CFB)
cipher.encrypt
cipher.key = KEY
iv = cipher.random_iv
encrypted = cipher.update(MESSAGE)+cipher.final
puts Base64.strict_encode64(iv)+'|'+Base64.strict_encode64(encrypted.encode)
decrypt.rb
require 'openssl'
require 'base64'
KEY = 'sekrit_key123456' * 2 # key needs to be the right length
encrypted_message = STDIN.read.strip
parts = encrypted_message.split('|')
iv = Base64.strict_decode64(parts[0])
encrypted = Base64.strict_decode64(parts[1])
decipher = OpenSSL::Cipher::AES256.new(:CFB)
decipher.decrypt
decipher.key = KEY
decipher.iv = iv
message = decipher.update(encrypted)+decipher.final
if message.eql?("My Name is Rabbit and I don't know anything!")
print '.'
else
puts
puts encrypted_message
puts message
end
Also notice that random_iv already assigns iv to cipher, so you don't need to (see source under http://apidock.com/ruby/v1_9_3_125/OpenSSL/Cipher/random_iv ).