SSAP

Stateless SAP (scale and perturbation) is rust library for a one way vector encryption based on SAP scheme as as described in Approximate Distance-Comparision Preserving Symmetric Encryption.

SSAP deviates from SAP in that the use of a psuedorandom function (PRF) is removed.

1. Rather than using a key K to generate a psuedorandom vector from a multivariate normal distribution for pertubation, we store a normalised vector as a key to remove the reliance on PRF.
2. Rather than storing a random factor n to generate a psuderandom scale factor x' the pertubation vector, we ommit to store it and generate x' at random. Since x' is a f32 randomly sampled from 0 to 1 which means there's a one in 16.7 million chance it can be guessed.

Included in this library is an implementation of the original SAP scheme as described in Approximate Distance Comparison Preserving Symmetric Encryption.

Usage

SAP

pub fn encrypt_decrypt_round_trip() {
    let value = create_random_vector(10);
    let seed = EncryptionSeed::new(5.0, 8);
    let mut sap = SAP::new(0.5);
    let ciphered = sap.encrypt(seed.clone(), value.clone());
    let deciphered = sap.decrypt(seed, ciphered);

    let is_equal = is_approximately_equal(value.clone(), deciphered.clone());
    assert!(
        is_equal,
        "Expect value equal deciphered. However got\nx: {:?}\ny: {:?}",
        value, deciphered
    )
}

SSAP

pub fn encrypt_with_key(){
    let plain_text = vec![0.02132726, -0.06046767, 0.018071115, 0.016465398];
    let seed = HashKey::new(4, 0.05, 2.0);
    let ciphert_text = hash(&seed, x);
    assert!(plain_text != cipher_text);
}