Class: Axlsx::MsOffCrypto

Inherits:
Object
  • Object
show all
Defined in:
lib/axlsx/util/ms_off_crypto.rb

Overview

The MsOffCrypto class implements ECMA-367 encryption based on the MS-OFF-CRYPTO specification

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(file_name, pwd) ⇒ MsOffCrypto

Creates a new MsOffCrypto Object

Parameters:

  • file_name (String) —

    the location of the file you want to encrypt

  • pwd (String) —

    the password to use when encrypting the file



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 14

def initialize(file_name, pwd)
  self.password = pwd
  self.file_name = file_name
end

Instance Attribute Details

#file_name ⇒ String

retruns the file name of the archive to be encrypted

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 38

def file_name
  @file_name
end

#password ⇒ String

returns the raw password used in encryption

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 27

def password
  @password
end

Instance Method Details

#create_encryption_info ⇒ String

Generates an encryption info structure

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 105

def create_encryption_info
  header = [3, 0, 2, 0] # version
  # Header flags copy
  header.concat [0x24, 0, 0, 0] #flags -- VERY UNSURE ABOUT THIS STILL
  # header.concat [0, 0, 0, 0] #unused
  header.concat [0xA4, 0, 0, 0] #length
  # Header
  header.concat  [0x24, 0, 0, 0] #flags again
  # header.concat [0, 0, 0, 0] #unused again,
  header.concat [0x0E, 0x66, 0, 0] #alg id
  header.concat [0x04, 0x80, 0, 0] #alg hash id
  header.concat [key.size, 0, 0, 0] #key size
  header.concat [0x18, 0, 0, 0] #provider type
  # header.concat [0, 0, 0, 0] #reserved 1
  # header.concat [0, 0, 0, 0] #reserved 2
  header.concat [0xA0, 0xC7, 0xDC, 0x2, 0, 0, 0, 0]
  header.concat "Microsoft Enhanced RSA and AES Cryptographic Provider (Prototype)".bytes.to_a.pack('s*').bytes.to_a
  header.concat [0, 0] #null terminator

  #Salt Size
  header.concat [salt.bytes.to_a.size].pack('l').bytes.to_a
  #Salt
  header.concat salt.bytes.to_a.pack('c*').bytes.to_a
  # encryption verifier
  header.concat encrypted_verifier.bytes.to_a.pack('c*').bytes.to_a

  # verifier hash size -- MUST BE 32 bytes
  header.concat [verifier_hash.bytes.to_a.size].pack('l').bytes.to_a

  #encryption verifier hash
  header.concat encrypted_verifier_hash.bytes.to_a.pack('c*').bytes.to_a

  header.flatten!
  header.pack('c*')
end

#create_key ⇒ Object

2.3.4.7 ECMA-376 Document Encryption Key Generation (Standard Encryption)



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 148

def create_key
  sha = Digest::SHA1.new() << (salt + @password)
  (0..49999).each { |i| sha.update(i.to_s+sha.to_s) }
  key = sha.update(sha.to_s+'0').digest
  a = key.bytes.each_with_index.map { |item, i|  0x36 ^ item }
  x1 = Digest::SHA1.digest((a.concat Array.new(64 - key.size, 0x36)).to_s)
  a = key.bytes.each_with_index.map { |item, i| 0x5C ^ item }
  x2 = Digest::SHA1.digest( (a.concat Array.new(64 - key.size, 0x5C) ).to_s)
  x3 = x1 + x2
  x3.bytes.to_a[(0..31)].pack('c*')
end

#create_verifier_hash ⇒ Object

2.3.3



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 142

def create_verifier_hash
  vh = Digest::SHA1.digest(verifier)
  vh << Array.new(32 - vh.size, 0).join('')
end

#decrypt(data) ⇒ String

dencrypts the data proved

Parameters:

  • data (String)

Returns:

  • (String) —

    the dencrypted data



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 181

def decrypt(data)
  aes = OpenSSL::Cipher.new("AES-128-ECB")     
  aes.decrypt
  aes.key = key
  aes.update(data) << aes.final
end

#encrypt(data) ⇒ String

encrypts the data proved

Parameters:

  • data (String)

Returns:

  • (String) —

    the encrypted data



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 171

def encrypt(data)
  aes = OpenSSL::Cipher.new("AES-128-ECB")     
  aes.encrypt
  aes.key = key
  aes.update(data) << aes.final
end

#encrypt_package(file_name) ⇒ Object

size of unencrypted package? concated with encrypted package



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 97

def encrypt_package(file_name)      
  package = File.open(file_name, 'r')
  crypt_pack = encrypt(package.read)      
  [crypt_pack.size].pack('q') + crypt_pack
end

#encrypted_package ⇒ String

encrypts and returns the package specified by the file name

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 50

def encrypted_package
  @encrypted_package ||= encrypt_package(file_name)
end

#encrypted_verifier ⇒ String

returns the verifier encrytped

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 74

def encrypted_verifier
  @encrypted_verifier ||= encrypt(verifier)
end

#encrypted_verifier_hash ⇒ String

returns the verifier hash encrypted

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 80

def encrypted_verifier_hash
  @encrypted_verifier_hash ||= encrypt(verifier_hash)
end

#encryption_info ⇒ String

returns the encryption info for this instance of ms-off-crypto

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 56

def encryption_info 
  @encryption_info ||= create_encryption_info
end

#key ⇒ String

returns an encryption key

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 92

def key 
  @key ||= create_key
end

#salt ⇒ String

returns a random salt

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 62

def salt
  @salt ||= Digest::SHA1.digest(rand(16**16).to_s)
end

#save ⇒ Object

Generates a new CBF file based on this instance of ms-off-crypto and overwrites the unencrypted file.



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# File 'lib/axlsx/util/ms_off_crypto.rb', line 20

def save
  cfb = Cbf.new(self)
  cfb.save
end

#verifier ⇒ String

returns a random verifier

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 68

def verifier 
  @verifier ||= rand(16**16).to_s
end

#verifier_hash ⇒ String

returns a verifier hash

Returns:

  • (String) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 86

def verifier_hash
  @verifier_hash ||= create_verifier_hash
end

#verify_password ⇒ Boolean

ensures that the a hashed decryption of the encryption verifier matches the decrypted verifier hash.

Returns:

  • (Boolean) 


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# File 'lib/axlsx/util/ms_off_crypto.rb', line 162

def verify_password
  v = Digest::SHA1.digest decrypt(@encrypted_verifier)
  vh = decrypt(@encrypted_verifier_hash)
  vh[0..15] == v[0..15]
end