lib/wechat/cipher.rb
# frozen_string_literal: true
module Wechat
module Cipher
BLOCK_SIZE = 32
CIPHER = 'AES-256-CBC'
def encrypt(plain, encoding_aes_key)
cipher = OpenSSL::Cipher.new(CIPHER)
cipher.encrypt
cipher.padding = 0
key_data = Base64.decode64("#{encoding_aes_key}=")
cipher.key = key_data
cipher.iv = [key_data].pack('H*')
cipher.update(plain) + cipher.final
end
def decrypt(msg, encoding_aes_key)
cipher = OpenSSL::Cipher.new(CIPHER)
cipher.decrypt
cipher.padding = 0
key_data = Base64.decode64("#{encoding_aes_key}=")
cipher.key = key_data
cipher.iv = [key_data].pack('H*')
plain = cipher.update(msg) + cipher.final
decode_padding(plain)
end
# app_id or corp_id
def pack(content, app_id)
random = SecureRandom.hex(8)
text = content.dup.force_encoding('ASCII-8BIT')
msg_len = [text.length].pack('N')
encode_padding("#{random}#{msg_len}#{text}#{app_id}")
end
def unpack(msg)
msg = decode_padding(msg)
msg_len = msg[16, 4].reverse.unpack1('V')
content = msg[20, msg_len]
app_id = msg[(msg_len + 20)..-1]
[content, app_id]
end
private
def encode_padding(data)
length = data.bytes.length
amount_to_pad = BLOCK_SIZE - (length % BLOCK_SIZE)
amount_to_pad = BLOCK_SIZE if amount_to_pad.zero?
padding = ([amount_to_pad].pack('c') * amount_to_pad)
data + padding
end
def decode_padding(plain)
pad = plain.bytes[-1]
# no padding
pad = 0 if pad < 1 || pad > BLOCK_SIZE
plain[0...(plain.length - pad)]
end
end
end