Skip to main content

streaming_encryption

🔐 Stream Encrypt/Decrypt Files with OpenSSL Cipher Streams​

For large-file encryption without buffering entire files, chain Ruby’s OpenSSL::Cipher with IO streaming. This keeps memory usage constant and integrates with any IO object.

require 'openssl'

cipher = OpenSSL::Cipher.new('aes-256-gcm')
cipher.encrypt
key = cipher.random_key
iv  = cipher.random_iv

encrypted = File.open('secret.enc', 'wb')
encrypted.write(iv)

iobuf = ''
File.open('secret.tar.gz', 'rb') do |input|
  while input.read(4096, iobuf)
    encrypted.write(cipher.update(iobuf))
  end
end
encrypted.write(cipher.final)
encrypted.close

Use similar logic with cipher.auth_tag to append GCM authentication tag. On decryption, read iv, set cipher.decrypt, and stream through cipher.update + cipher.final.