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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)
@username = username
@password = password
@salt = bigrand(10).hex
@multiplier = multiplier # let's cache it
calculate_verifier
end
def authenticate(server, username, password)
x = calculate_x(username, password, salt)
a = bigrand(32).hex
aa = modpow(GENERATOR, a, PRIME_N) # A = g^a (mod N)
bb, u = server.initialize_auth(aa)
client_s = calculate_client_s(x, a, bb, u)
server.authenticate(aa, client_s)
end
protected
def calculate_verifier
x = calculate_x(@username, @password, @salt)
@verifier = modpow(GENERATOR, x, PRIME_N)
end
def calculate_x(username, password, salt)
shex = '%x' % [salt]
spad = if shex.length.odd? then '0' else '' end
sha1_hex(spad + shex + sha1_str([username, password].join(':'))).hex
end
def calculate_client_s(x, a, bb, u)
base = bb
base += PRIME_N * @multiplier
base -= modpow(GENERATOR, x, PRIME_N) * @multiplier
base = base % PRIME_N
modpow(base, x * u + a, PRIME_N)
end
end
end
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