Class: H2C::M2C::ISOGeny::Secp256k1

Inherits:
Object
  • Object
show all
Defined in:
lib/h2c/m2c/isogeny/secp256k1.rb

Overview

3-isogeny map for secp256k1 www.ietf.org/archive/id/draft-irtf-cfrg-hash-to-curve-16.html#appendix-E.1

Constant Summary collapse

X_NUM = 
[
  0x8e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38daaaaa8c7,
  0x7d3d4c80bc321d5b9f315cea7fd44c5d595d2fc0bf63b92dfff1044f17c6581,
  0x534c328d23f234e6e2a413deca25caece4506144037c40314ecbd0b53d9dd262,
  0x8e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38e38daaaaa88c
].freeze
X_DEN = 
[
  0xd35771193d94918a9ca34ccbb7b640dd86cd409542f8487d9fe6b745781eb49b,
  0xedadc6f64383dc1df7c4b2d51b54225406d36b641f5e41bbc52a56612a8c6d14,
  1,
  0
].freeze
Y_NUM = 
[
  0x4bda12f684bda12f684bda12f684bda12f684bda12f684bda12f684b8e38e23c,
  0xc75e0c32d5cb7c0fa9d0a54b12a0a6d5647ab046d686da6fdffc90fc201d71a3,
  0x29a6194691f91a73715209ef6512e576722830a201be2018a765e85a9ecee931,
  0x2f684bda12f684bda12f684bda12f684bda12f684bda12f684bda12f38e38d84
].freeze
Y_DEN = 
[
  0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffefffff93b,
  0x7a06534bb8bdb49fd5e9e6632722c2989467c1bfc8e8d978dfb425d2685c2573,
  0x6484aa716545ca2cf3a70c3fa8fe337e0a3d21162f0d6299a7bf8192bfd2a76f,
  1
].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Secp256k1

Returns a new instance of Secp256k1.



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# File 'lib/h2c/m2c/isogeny/secp256k1.rb', line 35

def initialize
  @e0 = ECDSA::Group::Secp256k1_3ISO
  @e1 = ECDSA::Group::Secp256k1
end

Instance Attribute Details

#e0 ⇒ Object (readonly)

Returns the value of attribute e0.



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# File 'lib/h2c/m2c/isogeny/secp256k1.rb', line 8

def e0
  @e0
end

#e1 ⇒ Object (readonly)

Returns the value of attribute e1.



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# File 'lib/h2c/m2c/isogeny/secp256k1.rb', line 8

def e1
  @e1
end

Instance Method Details

#map(x, y) ⇒ Object 



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# File 'lib/h2c/m2c/isogeny/secp256k1.rb', line 40

def map(x, y)
  f = e0.field

  x_num = 0
  x_den = 0
  y_num = 0
  y_den = 0
  3.step(0, -1) do |i|
    x_num = f.mod(x_num * x + X_NUM[i])
    x_den = f.mod(x_den * x + X_DEN[i])
    y_num = f.mod(y_num * x + Y_NUM[i])
    y_den = f.mod(y_den * x + Y_DEN[i])
  end
  xx = f.mod(x_num * f.inverse(x_den))
  yy = f.mod(y * (y_num * f.inverse(y_den)))
  [xx, yy]
end