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require 'digest'
require 'openssl'
module SRP
module Util
# constants both sides know
# in this case taken from srp-js
PRIME_N = <<-EOS.split.join.hex
115b8b692e0e045692cf280b436735c77a5a9e8a9e7ed56c965f87db5b2a2ece3
EOS
BIG_PRIME_N = <<-EOS.split.join.hex # 1024 bits modulus (N)
eeaf0ab9adb38dd69c33f80afa8fc5e86072618775ff3c0b9ea2314c9c25657
6d674df7496ea81d3383b4813d692c6e0e0d5d8e250b98be48e495c1d6089da
d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
7ec68edbc3c05726cc02fd4cbf4976eaa9afd5138fe8376435b9fc61d2fc0eb
06e3
EOS
GENERATOR = 2 # g
def hn_xor_hg
byte_xor_hex(sha256_int(BIG_PRIME_N), sha256_int(GENERATOR))
end
# a^n (mod m)
def modpow(a, n, m = BIG_PRIME_N)
r = 1
while true
r = r * a % m if n[0] == 1
n >>= 1
return r if n == 0
a = a * a % m
end
end
# Hashes the (long) int args
def sha256_int(*args)
sha256_hex(*args.map{|a| "%02x" % a})
end
# Hashes the hex args
def sha256_hex(*args)
h = args.join('')
sha256_str([h].pack('H*'))
end
def sha256_str(s)
Digest::SHA2.hexdigest(s)
end
def bigrand(bytes)
OpenSSL::Random.random_bytes(bytes).unpack("H*")[0]
end
def multiplier
@k ||= calculate_multiplier
end
protected
def calculate_multiplier
sha256_int(BIG_PRIME_N, GENERATOR).hex
end
# turn two hex strings into byte arrays and xor them
#
# returns byte array
def byte_xor_hex(a, b)
a = [a].pack('H*')
b = [b].pack('H*')
a.bytes.each_with_index.map do |a_byte, i|
(a_byte ^ (b[i] || 0)).chr
end.join
end
end
end
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