Overview

GordianKnot can be personalised to ensure differing securitySpaces. The personalisation is achieved via a SecurityPhrase which is processed via a set of digests to produce two 512-bit arrays (I and IV) which are then utilised in the various algorithms.

I is often split into 16 integers written as I₁ through I₁₆. Similarly IV is often split into 4 128-bit arrays written as IV₁ through IV₄

Sample

                /* Access factory using security phrase */
                final char[] mySecurityPhrase = ...
                final GordianFactory myBaseFactory = GordianGenerator.createFactory(mySecurityPhrase);
            

Generation

The personalisation algorithm is as follows.

1. Initialise I and IV to all zeroes
2. Create an array of all available digests that have an output length of 512-bits.
3. Initialise all digests with a constant value followed by the security phrase
4. Finish all digests, creating an array R of the hashResults and xor each of these hashes into I
5. Loop for 2K iterations.
   1. Update each digest with ALL the elements of R
   2. Finish each digest, updating its hash in R and xor-ing into I
6. Repeat above loop for 2K iterations, xor-ing results into IV instead of I.
   1. Update each digest with ALL the elements of R
   2. Finish each digest, updating its hash in R and xor-ing into I

Seeded Random

Several algorithms in GordianKnot require selection of various algorithms in a deterministic fashion based on a 4-byte seed S. This is performed by creating a 6-byte seed from the combination of the 4-byte seed and one of the I_n values, specific to the algorithm. This 6-byte seed in used to instantiate an instance of the deterministic Random class and algorithm selection is performed via this seeded Random instance.

Key Derivation

The key derivation algorithm that generates a key K_A for an algorithm A from a secret S and vector V is as follows.

1. Obtain a seed X from the first 4 bytes of V and obtain a seeded random R using X and I₁
2. Obtain a set of two distinct HMACs H_M and H_A from the seededRandom R
3. Initialise both HMac with a key of secret S
4. Repeat the following loop until sufficient bits have been generated. Start with C = 0
   1. Initialise result to all zeros
   2. Update both Macs with I and IV
   3. Update both Macs with A, keyLength and C
   4. Set input D_M and D_A to V
   5. Loop for 16 iterations.
      1. Update H_A with D_A
      2. Calculate D_A as the hash result of H_A
      3. Update H_M with D_M and with D_A
      4. Calculate D_M as the hash result of H_M
      5. Xor D_M into the result
   6. Increment C and repeat if necessary.