Class: Noise::Functions::DH::Secp256k1

Inherits:
Object
  • Object
show all
Defined in:
lib/noise/functions/dh/secp256k1.rb

Constant Summary collapse

DHLEN =

Length of a compressed secp256k1 point. libsecp256k1 also accepts the 65-byte uncompressed form, but Noise exchanges only the compressed one.

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Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Secp256k1

Returns a new instance of Secp256k1.



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# File 'lib/noise/functions/dh/secp256k1.rb', line 13

def initialize
  Noise.optional_dependency!('secp256k1')
end

Class Method Details

.from_private(private_key) ⇒ Object 



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# File 'lib/noise/functions/dh/secp256k1.rb', line 47

def self.from_private(private_key)
  group = ECDSA::Group::Secp256k1
  scalar = ECDSA::Format::IntegerOctetString.decode(private_key)
  point = group.generator.multiply_by_scalar(scalar)
  Noise::Key.new(private_key, ECDSA::Format::PointOctetString.encode(point, compression: true))
end

Instance Method Details

#dh(private_key, public_key) ⇒ Object

Computes the ECDH shared secret for the given remote public key.

A point that is not on the curve makes libsecp256k1 raise Secp256k1::AssertError, while a public key of any other length raises ArgumentError before the point is even parsed. Both are translated to InvalidPublicKeyError, matching the other DH functions. The length is checked here rather than left to the gem so that ArgumentError raised for a malformed private key keeps propagating as itself.



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# File 'lib/noise/functions/dh/secp256k1.rb', line 34

def dh(private_key, public_key)
  raise Noise::Exceptions::InvalidPublicKeyError, public_key unless public_key.bytesize == DHLEN

  key = ::Secp256k1::PublicKey.new(pubkey: public_key, raw: true)
  key.ecdh(private_key)
rescue ::Secp256k1::AssertError
  raise Noise::Exceptions::InvalidPublicKeyError, public_key
end

#dhlen ⇒ Object 



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# File 'lib/noise/functions/dh/secp256k1.rb', line 43

def dhlen
  DHLEN
end

#generate_keypair ⇒ Object 



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# File 'lib/noise/functions/dh/secp256k1.rb', line 17

def generate_keypair
  group = ECDSA::Group::Secp256k1
  private_key = 1 + SecureRandom.random_number(group.order - 1)
  public_key = group.generator.multiply_by_scalar(private_key)
  Noise::Key.new(
    ECDSA::Format::IntegerOctetString.encode(private_key, 32),
    ECDSA::Format::PointOctetString.encode(public_key, compression: true)
  )
end