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Insecure encryption algorithm - Perfect Forward Secrecy


Implementation of a secure and robust encryption algorithm with Perfect Forward Secrecy (PFS)


  • Usage of Ruby for building dynamic and object-oriented applications
  • Usage of OpenSSL for secure communication and encryption


Non compliant code

require 'openssl'

cipher =, :CBC)
key = cipher.random_key
iv = cipher.random_iv

buf = ""
buf << cipher.update('This is a vulnerable message')
buf <<

The above code snippet is an example of using an insecure encryption algorithm in a Ruby on Rails backend application.

The OpenSSL::Cipher::AES class is being used to create a new cipher object with a 128 bit key size and Cipher Block Chaining (CBC) mode. Then, the encrypt method is called on this cipher object to set it up for encryption.

A random key is generated using the random_key method and a random initialization vector (IV) is generated using the random_iv method. These are used as the key and IV for the encryption process.

Finally, a message ('This is a vulnerable message') is encrypted using the update method and the final method. The encrypted message is stored in the buf variable.

The vulnerability lies in the fact that the same key is used for all messages. If an attacker is able to compromise this key, they will be able to decrypt all messages encrypted with this key. This is in violation of the Perfect Forward Secrecy (PFS) principle, which states that the compromise of a single key should not lead to the compromise of all messages.


  • Replace the insecure encryption algorithm with a secure one that supports Perfect Forward Secrecy (PFS).
  • Use a strong and secure key generation method to generate the encryption key.
  • Ensure that the encryption key is securely stored and protected.
  • Implement a secure method for generating the initialization vector (IV).
  • Ensure that the IV is securely stored and protected.
  • Implement a secure mode of operation for the encryption algorithm, such as GCM (Galois/Counter Mode) or CTR (Counter Mode).
  • Regularly update the encryption algorithm and libraries to stay up-to-date with the latest security patches and improvements.
  • Regularly rotate the encryption keys to minimize the impact of a potential compromise.
  • Implement proper key management practices, such as using a key management system or hardware security module (HSM) to securely store and manage the encryption keys.
  • Perform regular security audits and penetration testing to identify and address any potential vulnerabilities in the encryption implementation.

Compliant code

require 'openssl'

cipher ='aes-256-gcm')
key = cipher.random_key
iv = cipher.random_iv

# Store these for later
cipher_key = key
cipher_iv = iv

# Create a new cipher for decryption
decipher ='aes-256-gcm')
decipher.key = cipher_key
decipher.iv = cipher_iv

# Encrypt the data
encrypted = cipher.update('This is a secure message') +

# Decrypt the data
plain = decipher.update(encrypted) +

The updated code now uses the AES-256-GCM encryption algorithm, which is currently considered secure and supports Perfect Forward Secrecy (PFS).

The cipher.encrypt and cipher.decrypt methods are used to set the cipher mode to encryption and decryption respectively.

The cipher.random_key and cipher.random_iv methods are used to generate a random key and initialization vector (IV) for the encryption and decryption process. These are securely stored for later use.

The cipher.update method is used to encrypt the data, and the decipher.update method is used to decrypt the data. The and methods are used to finalize the encryption and decryption process.

This code ensures that even if a single key is compromised, previous communication cannot be decrypted, thus providing Perfect Forward Secrecy.

Remember to securely store the key and IV, rotate them regularly, and use a secure method for their generation. Also, keep your encryption libraries up to date and perform regular security audits to identify potential vulnerabilities.