Class: MLKEM::Core::KPKE

Inherits:
Object
  • Object
show all
Defined in:
lib/ml_kem/core/k_pke.rb

Overview

Implements the Public Key Encryption (K-PKE) as specified in ML-KEM (Kyber). Provides methods for key generation, encryption, and decryption using lattice-based NTT arithmetic.

Since:

  • 0.1.0

Instance Method Summary collapse

Constructor Details

#initialize(k, eta1, eta2, du, dv, q = Constants::Q) ⇒ KPKE

Initializes the KPKE engine with given parameters.

Parameters:

  • k (Integer) —

    Security level (2, 3, or 4 for ML-KEM-512/768/1024)

  • eta1 (Integer) —

    Noise parameter for secret and error

  • eta2 (Integer) —

    Noise parameter for encryption errors

  • du (Integer) —

    Compression bits for u

  • dv (Integer) —

    Compression bits for v

  • q (Integer) (defaults to: Constants::Q) —

    Prime modulus

Since:

  • 0.1.0



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# File 'lib/ml_kem/core/k_pke.rb', line 21

def initialize(k, eta1, eta2, du, dv, q = Constants::Q)
  @k = k
  @eta1 = eta1
  @eta2 = eta2
  @du = du
  @dv = dv
  @q = q

  @poly_ops = Math::Polynomial.new(@q)
  @ntt_ops = Math::NTT.new(@q)
  @sampling = Math::Sampling.new(@q)
end

Instance Method Details

#decrypt(dk_pke, c) ⇒ String

Decryption algorithm (Algorithm 15).

Parameters:

  • dk_pke (String) —

    Secret key

  • c (String) —

    Ciphertext

Returns:

  • (String) —

    Recovered message (32-byte encoded bitstring)

Since:

  • 0.1.0



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# File 'lib/ml_kem/core/k_pke.rb', line 144

def decrypt(dk_pke, c)
  c1 = c[0...(32 * @du * @k)]
  c2 = c[(32 * @du * @k)...(32 * (@du * @k + @dv))]

  up = Array.new(@k)
  @k.times do |i|
    up[i] = @poly_ops.decompress(@du,
            Math::ByteOperations.byte_decode(@du, c1[(32 * @du * i)...(32 * @du * (i + 1))], @q))
  end

  vp = @poly_ops.decompress(@dv, Math::ByteOperations.byte_decode(@dv, c2, @q))

  s = Array.new(@k)
  @k.times do |i|
    s[i] = Math::ByteOperations.byte_decode(12, dk_pke[(384 * i)...(384 * (i + 1))], @q)
  end

  w = Array.new(256, 0)
  @k.times do |i|
    w = @poly_ops.add(w, @ntt_ops.multiply_ntts(s[i], @ntt_ops.ntt(up[i])))
  end
  w = @poly_ops.subtract(vp, @ntt_ops.inverse_ntt(w))

  Math::ByteOperations.byte_encode(1, @poly_ops.compress(1, w), @q)
end

#encrypt(ek_pke, m, r) ⇒ String

Encryption algorithm (Algorithm 14).

Parameters:

  • ek_pke (String) —

    Public key

  • m (String) —

    Message (32 bytes of encoded bits)

  • r (String) —

    Randomness (32-byte seed)

Returns:

  • (String) —

    Ciphertext

Since:

  • 0.1.0



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# File 'lib/ml_kem/core/k_pke.rb', line 80

def encrypt(ek_pke, m, r)
  n = 0

  t = Array.new(@k)
  @k.times do |i|
    t[i] = Math::ByteOperations.byte_decode(12, ek_pke[(384 * i)...(384 * (i + 1))], @q)
  end
  rho = ek_pke[(384 * @k)...(384 * @k + 32)]

  a = Array.new(@k) { Array.new(@k) }
  @k.times do |i|
    @k.times do |j|
      a[i][j] = @sampling.sample_ntt(rho + [j, i].pack('CC'))
    end
  end

  y = Array.new(@k)
  e1 = Array.new(@k)
  @k.times do |i|
    y[i] = @sampling.sample_poly_cbd(@eta1, Crypto::SymmetricPrimitives.prf(@eta1, r, n))
    n += 1
    e1[i] = @sampling.sample_poly_cbd(@eta2, Crypto::SymmetricPrimitives.prf(@eta2, r, n))
    n += 1
  end
  e2 = @sampling.sample_poly_cbd(@eta2, Crypto::SymmetricPrimitives.prf(@eta2, r, n))

  y.map! { |v| @ntt_ops.ntt(v) }

  u = Array.new(@k) { Array.new(256, 0) }
  @k.times do |i|
    @k.times do |j|
      u[i] = @poly_ops.add(u[i], @ntt_ops.multiply_ntts(a[j][i], y[j]))
    end
  end

  @k.times do |i|
    u[i] = @ntt_ops.inverse_ntt(u[i])
    u[i] = @poly_ops.add(u[i], e1[i])
  end

  mu = @poly_ops.decompress(1, Math::ByteOperations.byte_decode(1, m, @q))

  v = Array.new(256, 0)
  @k.times do |i|
    v = @poly_ops.add(v, @ntt_ops.multiply_ntts(t[i], y[i]))
  end
  v = @ntt_ops.inverse_ntt(v)
  v = @poly_ops.add(v, e2)
  v = @poly_ops.add(v, mu)

  c1 = ''
  @k.times do |i|
    c1 += Math::ByteOperations.byte_encode(@du, @poly_ops.compress(@du, u[i]), @q)
  end
  c2 = Math::ByteOperations.byte_encode(@dv, @poly_ops.compress(@dv, v), @q)

  c1 + c2
end

#keygen(d) ⇒ Array<String>

Key generation algorithm (Algorithm 13).

Parameters:

  • d (String) —

    Random seed (32 bytes)

Returns:

  • (Array<String>) —
    public_key, secret_key

    both as binary strings

Since:

  • 0.1.0



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# File 'lib/ml_kem/core/k_pke.rb', line 38

def keygen(d)
  rho, sig = Crypto::SymmetricPrimitives.g(d + [@k].pack('C'))
  n = 0

  a = Array.new(@k) { Array.new(@k) }
  @k.times do |i|
    @k.times do |j|
      a[i][j] = @sampling.sample_ntt(rho + [j, i].pack('CC'))
    end
  end

  s = Array.new(@k)
  e = Array.new(@k)
  @k.times do |i|
    s[i] = @sampling.sample_poly_cbd(@eta1, Crypto::SymmetricPrimitives.prf(@eta1, sig, n))
    n += 1
    e[i] = @sampling.sample_poly_cbd(@eta1, Crypto::SymmetricPrimitives.prf(@eta1, sig, n))
    n += 1
  end

  s.map! { |v| @ntt_ops.ntt(v) }
  e.map! { |v| @ntt_ops.ntt(v) }

  t = e.dup
  @k.times do |i|
    @k.times do |j|
      t[i] = @poly_ops.add(t[i], @ntt_ops.multiply_ntts(a[i][j], s[j]))
    end
  end

  ek_pke = Math::ByteOperations.byte_encode(12, t, @q) + rho
  dk_pke = Math::ByteOperations.byte_encode(12, s, @q)

  [ek_pke, dk_pke]
end