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require 'openssl'
require 'net/ssh/transport/identity_cipher'
module Net; module SSH; module Transport
# Implements a factory of OpenSSL cipher algorithms.
class CipherFactory
# Maps the SSH name of a cipher to it's corresponding OpenSSL name
SSH_TO_OSSL = {
"3des-cbc" => "des-ede3-cbc",
"blowfish-cbc" => "bf-cbc",
"aes256-cbc" => "aes-256-cbc",
"aes192-cbc" => "aes-192-cbc",
"aes128-cbc" => "aes-128-cbc",
"idea-cbc" => "idea-cbc",
"cast128-cbc" => "cast-cbc",
"rijndael-cbc@lysator.liu.se" => "aes-256-cbc",
"arcfour128" => "rc4",
"arcfour256" => "rc4",
"arcfour512" => "rc4",
"none" => "none"
}
# Ruby's OpenSSL bindings always return a key length of 16 for RC4 ciphers
# resulting in the error: OpenSSL::CipherError: key length too short.
# The following ciphers will override this key length.
KEY_LEN_OVERRIDE = {
"arcfour256" => 32,
"arcfour512" => 64
}
# Returns true if the underlying OpenSSL library supports the given cipher,
# and false otherwise.
def self.supported?(name)
ossl_name = SSH_TO_OSSL[name] or raise NotImplementedError, "unimplemented cipher `#{name}'"
return true if ossl_name == "none"
return OpenSSL::Cipher.ciphers.include?(ossl_name)
end
# Retrieves a new instance of the named algorithm. The new instance
# will be initialized using an iv and key generated from the given
# iv, key, shared, hash and digester values. Additionally, the
# cipher will be put into encryption or decryption mode, based on the
# value of the +encrypt+ parameter.
def self.get(name, options={})
ossl_name = SSH_TO_OSSL[name] or raise NotImplementedError, "unimplemented cipher `#{name}'"
return IdentityCipher if ossl_name == "none"
cipher = OpenSSL::Cipher::Cipher.new(ossl_name)
cipher.send(options[:encrypt] ? :encrypt : :decrypt)
cipher.padding = 0
cipher.iv = make_key(cipher.iv_len, options[:iv], options) if ossl_name != "rc4"
key_len = KEY_LEN_OVERRIDE[name] || cipher.key_len
cipher.key_len = key_len
cipher.key = make_key(key_len, options[:key], options)
cipher.update(" " * 1536) if ossl_name == "rc4"
return cipher
end
# Returns a two-element array containing the [ key-length,
# block-size ] for the named cipher algorithm. If the cipher
# algorithm is unknown, or is "none", 0 is returned for both elements
# of the tuple.
def self.get_lengths(name)
ossl_name = SSH_TO_OSSL[name]
return [0, 0] if ossl_name.nil? || ossl_name == "none"
cipher = OpenSSL::Cipher::Cipher.new(ossl_name)
key_len = KEY_LEN_OVERRIDE[name] || cipher.key_len
cipher.key_len = key_len
return [key_len, ossl_name=="rc4" ? 8 : cipher.block_size]
end
private
# Generate a key value in accordance with the SSH2 specification.
def self.make_key(bytes, start, options={})
k = start[0, bytes]
digester = options[:digester] or raise 'No digester supplied'
shared = options[:shared] or raise 'No shared secret supplied'
hash = options[:hash] or raise 'No hash supplied'
while k.length < bytes
step = digester.digest(shared + hash + k)
bytes_needed = bytes - k.length
k << step[0, bytes_needed]
end
return k
end
end
end; end; end
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