Class: Gala::PaymentToken

Inherits:
Object
  • Object
show all
Defined in:
lib/gala/payment_token.rb

Defined Under Namespace

Classes: InvalidSignatureError, MissingMerchantIdError

Constant Summary collapse

MERCHANT_ID_FIELD_OID = 
"1.2.840.113635.100.6.32"
LEAF_CERTIFICATE_OID = 
"1.2.840.113635.100.6.29"
INTERMEDIATE_CERTIFICATE_OID = 
"1.2.840.113635.100.6.2.14"
APPLE_ROOT_CERT = 
File.read(File.dirname(__FILE__) + "/resources/AppleRootCA-G3.pem")

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(token_attrs) ⇒ PaymentToken

Returns a new instance of PaymentToken.



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# File 'lib/gala/payment_token.rb', line 18

def initialize(token_attrs)
  self.version = token_attrs["version"]
  self.data = token_attrs["data"]
  self.signature = token_attrs["signature"]
  headers = token_attrs["header"]
  self.transaction_id = headers["transactionId"]
  self.ephemeral_public_key = headers["ephemeralPublicKey"]
  self.public_key_hash = headers["publicKeyHash"]
  self.application_data = headers["applicationData"]
end

Instance Attribute Details

#application_data ⇒ Object

Returns the value of attribute application_data.



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# File 'lib/gala/payment_token.rb', line 12

def application_data
  @application_data
end

#data ⇒ Object

Returns the value of attribute data.



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# File 'lib/gala/payment_token.rb', line 12

def data
  @data
end

#ephemeral_public_key ⇒ Object

Returns the value of attribute ephemeral_public_key.



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# File 'lib/gala/payment_token.rb', line 12

def ephemeral_public_key
  @ephemeral_public_key
end

#public_key_hash ⇒ Object

Returns the value of attribute public_key_hash.



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# File 'lib/gala/payment_token.rb', line 12

def public_key_hash
  @public_key_hash
end

#signature ⇒ Object

Returns the value of attribute signature.



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# File 'lib/gala/payment_token.rb', line 12

def signature
  @signature
end

#transaction_id ⇒ Object

Returns the value of attribute transaction_id.



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# File 'lib/gala/payment_token.rb', line 12

def transaction_id
  @transaction_id
end

#version ⇒ Object

Returns the value of attribute version.



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# File 'lib/gala/payment_token.rb', line 12

def version
  @version
end

Class Method Details

.chain_of_trust_verified?(leaf_cert, intermediate_cert, root_cert) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/gala/payment_token.rb', line 73

def chain_of_trust_verified?(leaf_cert, intermediate_cert, root_cert)
  trusted_certificate_store = OpenSSL::X509::Store.new.tap do |store|
    store.add_cert(root_cert)
    store.add_cert(intermediate_cert)
  end
  trusted_certificate_store.verify(leaf_cert)
end

.decrypt(encrypted_data, symmetric_key) ⇒ Object 



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# File 'lib/gala/payment_token.rb', line 112

def decrypt(encrypted_data, symmetric_key)
  # Initialization vector of 16 null bytes
  iv_length = 16
  # 0.chr => "\x00"
  iv = 0.chr * iv_length

  # Last 16 bytes (iv_length) of encrypted data
  tag = encrypted_data[-iv_length..-1]
  # Data without tag
  encrypted_data = encrypted_data[0..(-iv_length - 1)]

  cipher = OpenSSL::Cipher.new("aes-256-gcm").decrypt
  cipher.key = symmetric_key
  cipher.iv_len = iv_length
  cipher.iv = iv

  # Decipher without associated authentication data
  cipher.auth_tag = tag
  cipher.auth_data = ''

  cipher.update(encrypted_data) + cipher.final
end

.extract_merchant_id(certificate) ⇒ Object

Raises:



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# File 'lib/gala/payment_token.rb', line 81

def extract_merchant_id(certificate)
  merchant_id_field = certificate.extensions.find do |ext|
    ext.oid == MERCHANT_ID_FIELD_OID
  end
  raise MissingMerchantIdError unless merchant_id_field
  val = merchant_id_field.value
  val[2..(val.length - 1)]
end

.generate_shared_secret(private_key, ephemeral_public_key) ⇒ Object 



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# File 'lib/gala/payment_token.rb', line 90

def generate_shared_secret(private_key, ephemeral_public_key)
  public_ec = OpenSSL::PKey::EC.new(Base64.decode64(ephemeral_public_key))
  point = OpenSSL::PKey::EC::Point.new(private_key.group, public_ec.public_key.to_bn)
  private_key.dh_compute_key(point)
end

.generate_symmetric_key(merchant_id, shared_secret) ⇒ Object

Derive the symmetric key using the key derivation function described in NIST SP 800-56A, section 5.8.1

http://csrc.nist.gov/publications/nistpubs/800-56A/SP800-56A_Revision1_Mar08-2007.pdf



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# File 'lib/gala/payment_token.rb', line 98

def generate_symmetric_key(merchant_id, shared_secret)

  kdf_algorithm = "\x0D" + 'id-aes256-GCM'
  kdf_party_v = merchant_id.scan(/../).inject("") { |binary,hn| binary << hn.to_i(16).chr } # Converts each pair of hex characters into bytes in a string.
  kdf_info = kdf_algorithm + "Apple" + kdf_party_v

  digest = Digest::SHA256.new
  digest << 0.chr * 3
  digest << 1.chr
  digest << shared_secret
  digest << kdf_info
  digest.digest
end

.validate_signature(signature, ephemeral_public_key, data, transaction_id, application_data) ⇒ Object

Raises:



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# File 'lib/gala/payment_token.rb', line 44

def validate_signature(signature, ephemeral_public_key, data, transaction_id, application_data)
  # Ensure that the certificates contain the correct custom OIDs
  intermediate_cert = nil
  leaf_cert = nil
  p7 = OpenSSL::PKCS7.new(Base64.decode64(signature))
  p7.certificates.each {|c|
    c.extensions.each { |e|
      leaf_cert = c if e.oid == LEAF_CERTIFICATE_OID
      intermediate_cert = c if e.oid == INTERMEDIATE_CERTIFICATE_OID
    }
  }
  raise InvalidSignatureError, "Signature does not contain the correct custom OIDs." unless leaf_cert && intermediate_cert

  # Ensure that the root CA is the Apple Root CA - G3
  root_cert = OpenSSL::X509::Certificate.new(APPLE_ROOT_CERT)

  # Ensure that there is a valid X.509 chain of trust from the signature to the root CA
  raise InvalidSignatureError, "Unable to verify a valid chain of trust from signature to root certificate." unless chain_of_trust_verified?(leaf_cert, intermediate_cert, root_cert)

  #Ensure that the signature is a valid ECDSA signature
  unless application_data
    verification_string = Base64.decode64(ephemeral_public_key) + Base64.decode64(data) + [transaction_id].pack("H*")
    # verification_string = verification_string + application_data.pack("H*") if application_data
    store = OpenSSL::X509::Store.new
    verified = p7.verify([], store, verification_string, OpenSSL::PKCS7::NOVERIFY )
    raise InvalidSignatureError, "The given signature is not a valid ECDSA signature." unless verified
  end
end

Instance Method Details

#decrypt(certificate_pem, private_key_pem) ⇒ Object 



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# File 'lib/gala/payment_token.rb', line 29

def decrypt(certificate_pem, private_key_pem)
  self.class.validate_signature(signature, ephemeral_public_key, data, transaction_id, application_data)

  certificate = OpenSSL::X509::Certificate.new(certificate_pem)
  merchant_id = self.class.extract_merchant_id(certificate)
  private_key = OpenSSL::PKey::EC.new(private_key_pem)
  shared_secret = self.class.generate_shared_secret(private_key, ephemeral_public_key)
  symmetric_key = self.class.generate_symmetric_key(merchant_id, shared_secret)

  # Return JSON string, up to caller to parse
  self.class.decrypt(Base64.decode64(data), symmetric_key)
end