Module: Nuckle::Internals::Salsa20

Defined in:
lib/nuckle/internals/salsa20.rb

Overview

Salsa20 stream cipher family: Salsa20 core, HSalsa20, XSalsa20.

References:

Constant Summary collapse

MASK32 = 
0xFFFFFFFF
SIGMA = 
"expand 32-byte k".b.freeze
SIGMA_V4 = 
SIGMA.unpack("V4").freeze

Class Method Summary collapse

Class Method Details

.core(input) ⇒ String

Salsa20 core function: 20 rounds on 16 x 32-bit words. Returns the 64-byte output block.

Parameters:

  • input (String) —

    64-byte input block

Returns:

  • (String) —

    64-byte output block



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# File 'lib/nuckle/internals/salsa20.rb', line 24

def core(input)
  x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15 =
    input.unpack("V16")

  z0  = x0;  z1  = x1;  z2  = x2;  z3  = x3
  z4  = x4;  z5  = x5;  z6  = x6;  z7  = x7
  z8  = x8;  z9  = x9;  z10 = x10; z11 = x11
  z12 = x12; z13 = x13; z14 = x14; z15 = x15

  10.times do
    # Column rounds
    t = (z0  + z12) & MASK32; z4  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z4  + z0)  & MASK32; z8  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z8  + z4)  & MASK32; z12 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z12 + z8)  & MASK32; z0  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z5  + z1)  & MASK32; z9  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z9  + z5)  & MASK32; z13 ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z13 + z9)  & MASK32; z1  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z1  + z13) & MASK32; z5  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z10 + z6)  & MASK32; z14 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z14 + z10) & MASK32; z2  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z2  + z14) & MASK32; z6  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z6  + z2)  & MASK32; z10 ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z15 + z11) & MASK32; z3  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z3  + z15) & MASK32; z7  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z7  + z3)  & MASK32; z11 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z11 + z7)  & MASK32; z15 ^= ((t << 18) | (t >> 14)) & MASK32

    # Row rounds
    t = (z0  + z3)  & MASK32; z1  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z1  + z0)  & MASK32; z2  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z2  + z1)  & MASK32; z3  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z3  + z2)  & MASK32; z0  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z5  + z4)  & MASK32; z6  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z6  + z5)  & MASK32; z7  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z7  + z6)  & MASK32; z4  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z4  + z7)  & MASK32; z5  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z10 + z9)  & MASK32; z11 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z11 + z10) & MASK32; z8  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z8  + z11) & MASK32; z9  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z9  + z8)  & MASK32; z10 ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z15 + z14) & MASK32; z12 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z12 + z15) & MASK32; z13 ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z13 + z12) & MASK32; z14 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z14 + z13) & MASK32; z15 ^= ((t << 18) | (t >> 14)) & MASK32
  end

  [
    (z0  + x0)  & MASK32, (z1  + x1)  & MASK32, (z2  + x2)  & MASK32, (z3  + x3)  & MASK32,
    (z4  + x4)  & MASK32, (z5  + x5)  & MASK32, (z6  + x6)  & MASK32, (z7  + x7)  & MASK32,
    (z8  + x8)  & MASK32, (z9  + x9)  & MASK32, (z10 + x10) & MASK32, (z11 + x11) & MASK32,
    (z12 + x12) & MASK32, (z13 + x13) & MASK32, (z14 + x14) & MASK32, (z15 + x15) & MASK32,
  ].pack("V16")
end

.hsalsa20(key, nonce) ⇒ String

HSalsa20: derives a 32-byte subkey from a 32-byte key and 16-byte nonce. Returns words [0,5,10,15,6,7,8,9] from the NON-added state.

Parameters:

  • key (String) —

    32-byte key

  • nonce (String) —

    16-byte nonce

Returns:

  • (String) —

    32-byte subkey



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# File 'lib/nuckle/internals/salsa20.rb', line 92

def hsalsa20(key, nonce)
  k0, k1, k2, k3, k4, k5, k6, k7 = key.unpack("V8")
  n0, n1, n2, n3 = nonce.unpack("V4")
  s0, s1, s2, s3 = SIGMA_V4

  z0  = s0; z1  = k0; z2  = k1; z3  = k2
  z4  = k3; z5  = s1; z6  = n0; z7  = n1
  z8  = n2; z9  = n3; z10 = s2; z11 = k4
  z12 = k5; z13 = k6; z14 = k7; z15 = s3

  10.times do
    t = (z0  + z12) & MASK32; z4  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z4  + z0)  & MASK32; z8  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z8  + z4)  & MASK32; z12 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z12 + z8)  & MASK32; z0  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z5  + z1)  & MASK32; z9  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z9  + z5)  & MASK32; z13 ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z13 + z9)  & MASK32; z1  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z1  + z13) & MASK32; z5  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z10 + z6)  & MASK32; z14 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z14 + z10) & MASK32; z2  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z2  + z14) & MASK32; z6  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z6  + z2)  & MASK32; z10 ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z15 + z11) & MASK32; z3  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z3  + z15) & MASK32; z7  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z7  + z3)  & MASK32; z11 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z11 + z7)  & MASK32; z15 ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z0  + z3)  & MASK32; z1  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z1  + z0)  & MASK32; z2  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z2  + z1)  & MASK32; z3  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z3  + z2)  & MASK32; z0  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z5  + z4)  & MASK32; z6  ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z6  + z5)  & MASK32; z7  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z7  + z6)  & MASK32; z4  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z4  + z7)  & MASK32; z5  ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z10 + z9)  & MASK32; z11 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z11 + z10) & MASK32; z8  ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z8  + z11) & MASK32; z9  ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z9  + z8)  & MASK32; z10 ^= ((t << 18) | (t >> 14)) & MASK32

    t = (z15 + z14) & MASK32; z12 ^= ((t << 7)  | (t >> 25)) & MASK32
    t = (z12 + z15) & MASK32; z13 ^= ((t << 9)  | (t >> 23)) & MASK32
    t = (z13 + z12) & MASK32; z14 ^= ((t << 13) | (t >> 19)) & MASK32
    t = (z14 + z13) & MASK32; z15 ^= ((t << 18) | (t >> 14)) & MASK32
  end

  # Return words [0,5,10,15,6,7,8,9] — the diagonal + second row
  [z0, z5, z10, z15, z6, z7, z8, z9].pack("V8")
end

.salsa20_xor(key, nonce, message) ⇒ String

Salsa20 stream XOR with 32-byte key and 16-byte nonce/counter.

Parameters:

  • key (String) —

    32-byte key

  • nonce (String) —

    16-byte (8-byte nonce + 8-byte counter, LE)

  • message (String) —

    plaintext/ciphertext

Returns:

  • (String) —

    XOR’d output



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# File 'lib/nuckle/internals/salsa20.rb', line 168

def salsa20_xor(key, nonce, message)
  k0, k1, k2, k3, k4, k5, k6, k7 = key.unpack("V8")
  n0, n1, n2, n3 = nonce.unpack("V4")
  s0, s1, s2, s3 = SIGMA_V4

  msg    = message.b
  len    = msg.bytesize
  out    = String.new(capacity: len, encoding: Encoding::BINARY)
  offset = 0

  while offset < len
    # Build + run Salsa20 core inline
    block = core([
      s0, k0, k1, k2,
      k3, s1, n0, n1,
      n2, n3, s2, k4,
      k5, k6, k7, s3,
    ].pack("V16"))

    # XOR message bytes with keystream block
    remaining = len - offset
    take      = remaining < 64 ? remaining : 64

    if take == 64
      # Fast path: XOR 8 x uint64
      m = msg.byteslice(offset, 64).unpack("Q<8")
      b = block.unpack("Q<8")
      out << [m[0] ^ b[0], m[1] ^ b[1], m[2] ^ b[2], m[3] ^ b[3],
              m[4] ^ b[4], m[5] ^ b[5], m[6] ^ b[6], m[7] ^ b[7]].pack("Q<8")
    else
      # Tail: XOR byte-by-byte
      m = msg.byteslice(offset, take).unpack("C*")
      b = block.unpack("C*")
      take.times { |i| m[i] ^= b[i] }
      out << m.pack("C*")
    end
    offset += take

    # Increment 64-bit counter (words n2, n3)
    counter  = n2 | (n3 << 32)
    counter += 1
    n2       = counter & MASK32
    n3       = (counter >> 32) & MASK32
  end

  out
end

.xsalsa20_stream(key, nonce, length) ⇒ String

Generate XSalsa20 keystream (no XOR, just the stream bytes).

Parameters:

  • key (String) —

    32-byte key

  • nonce (String) —

    24-byte nonce

  • length (Integer) —

    number of bytes to generate

Returns:

  • (String) —

    keystream bytes



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# File 'lib/nuckle/internals/salsa20.rb', line 223

def xsalsa20_stream(key, nonce, length)
  xsalsa20_xor(key, nonce, "\x00".b * length)
end

.xsalsa20_xor(key, nonce, message) ⇒ String

XSalsa20 stream XOR: encrypts/decrypts message using 32-byte key and 24-byte nonce.

Parameters:

  • key (String) —

    32-byte key

  • nonce (String) —

    24-byte nonce

  • message (String) —

    plaintext/ciphertext

Returns:

  • (String) —

    XOR’d output (same length as message)



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# File 'lib/nuckle/internals/salsa20.rb', line 155

def xsalsa20_xor(key, nonce, message)
  subkey    = hsalsa20(key, nonce.byteslice(0, 16))
  sub_nonce = (nonce.byteslice(16, 8) + "\x00\x00\x00\x00\x00\x00\x00\x00").b
  salsa20_xor(subkey, sub_nonce, message)
end