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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
# a^n (mod m)
def modpow(a, n, m)
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
def sha256_hex(h)
Digest::SHA2.hexdigest([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
n = BIG_PRIME_N
g = GENERATOR
nhex = '%x' % n
ghex = '0%x' % g
hashin = [nhex].pack('H*') + [ghex].pack('H*')
sha256_str(hashin).hex
end
def calculate_m(aa, bb, s)
hashin = '%x%x%x' % [aa, bb, s]
sha256_str(hashin).hex
end
def calculate_u(aa, bb, n)
nlen = 2 * ((('%x' % [n]).length * 4 + 7) >> 3)
aahex = '%x' % [aa]
bbhex = '%x' % [bb]
return sha256_str("%x%x" % [aa, bb]).hex
end
end
end
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