Basic encrypt and decrypt Strings in Ruby with deterministic salt or IV, generate and store random salt and IV in production

encrypt_decrypt.rb

require 'openssl'

class String
  CIPHER_NAME   = 'aes-256-cbc'.freeze
  PBKDF_ITER    = 200_000
  KEY_LEN       = 32  # 256 bits
  SALT_CONST    = "fixed-global-salt-v1".freeze
  IV_SALT_CONST = "fixed-iv-salt-v1".freeze

  def encrypt(password)
    cipher = OpenSSL::Cipher.new(CIPHER_NAME)
    cipher.encrypt

    # derive key
    key = OpenSSL::PKCS5.pbkdf2_hmac(
      password,
      SALT_CONST,
      PBKDF_ITER,
      KEY_LEN,
      "sha256"
    )
    cipher.key = key

    # derive deterministic IV (no storage needed)
    iv = OpenSSL::PKCS5.pbkdf2_hmac(
      password,
      IV_SALT_CONST,
      PBKDF_ITER,
      cipher.iv_len,
      "sha256"
    )
    cipher.iv = iv

    ciphertext = cipher.update(self) + cipher.final

    # encode as IV || CIPHERTEXT (hex)
    (iv + ciphertext).unpack1("H*").upcase
  end

  def decrypt(password)
    raw = [self].pack("H*")

    cipher = OpenSSL::Cipher.new(CIPHER_NAME)
    cipher.decrypt

    key = OpenSSL::PKCS5.pbkdf2_hmac(
      password,
      SALT_CONST,
      PBKDF_ITER,
      KEY_LEN,
      "sha256"
    )
    cipher.key = key

    iv_len = cipher.iv_len
    iv = raw[0, iv_len]
    ct = raw[iv_len..-1]

    cipher.iv = iv

    cipher.update(ct) + cipher.final
  end
end



puts plain = 'confidential'           # confidential
puts key = 'secret'                   # secret
puts cipher = plain.encrypt(key)      # 5C6D4C5FAFFCF09F271E01C5A132BE89

puts cipher.decrypt('guess')          # raises OpenSSL::Cipher::CipherError
puts cipher.decrypt(key)              # confidential

avoiding key must be 24 bytes

def encrypt(key)
        cipher = OpenSSL::Cipher.new("aes-256-cbc").encrypt
        cipher.key = Digest::MD5.hexdigest key
        s = cipher.update(self) + cipher.final

        s.unpack('H*')[0].upcase
      end

      def decrypt(key)
        cipher = OpenSSL::Cipher.new('aes-256-cbc').decrypt
        cipher.key = Digest::MD5.hexdigest key
        s = [self].pack("H*").unpack("C*").pack("c*")

        cipher.update(s) + cipher.final
      end

thanks, works perfectly!