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require File.expand_path(File.dirname(__FILE__) + '/util')
module SRP
class Client
include Util
attr_reader :salt, :verifier
def initialize(username, password, salt = nil)
@username = username
@password = password
@salt = (salt || bigrand(4)).hex
@multiplier = multiplier # let's cache it
calculate_verifier
end
def authenticate(server, username, password)
x = calculate_x(username, password)
a = bigrand(32).hex
aa = modpow(GENERATOR, a, BIG_PRIME_N) # A = g^a (mod N)
bb = server.handshake(username, aa)
u = calculate_u(aa, bb)
client_s = calculate_client_s(x, a, bb, u)
server.validate(calculate_m(aa, bb, client_s))
end
protected
def calculate_verifier
x = calculate_x
@verifier = modpow(GENERATOR, x, BIG_PRIME_N)
@verifier
end
def calculate_x(username = @username, password = @password)
shex = '%x' % [@salt]
inner = sha256_str([username, password].join(':'))
sha256_hex(shex, inner).hex
end
def calculate_client_s(x, a, bb, u)
base = bb
base += BIG_PRIME_N * @multiplier
base -= modpow(GENERATOR, x, BIG_PRIME_N) * @multiplier
base = base % BIG_PRIME_N
modpow(base, x * u + a, BIG_PRIME_N)
end
end
end
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