Class: KmsTools::Decrypter

Inherits:
Base
  • Object
show all
Defined in:
lib/kms-tools/decrypter.rb

Overview

Provides low-level decryption functionality for kms-tools

Author:

  • Matt Kriegers

Constant Summary

Constants inherited from Base

Base::DEFAULT_REGION

Instance Attribute Summary

Attributes inherited from Base

#kms, #master_key

Instance Method Summary collapse

Methods inherited from Base

#available_aliases, #from_64, #initialize, #master_key_arn, #master_key_id, #region, #to_64, #to_s64, #use_key_alias=

Constructor Details

This class inherits a constructor from KmsTools::Base

Instance Method Details

#decrypt_string(str) ⇒ String

Decrypt base64 encoded ciphertext that was encrypted directly with a customer master key

Parameters:

  • str (String) —

    Base64 encoded ciphertext

Returns:

  • (String) —

    Binary plaintext



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# File 'lib/kms-tools/decrypter.rb', line 10

def decrypt_string(str)
  kms.decrypt({:ciphertext_blob => from_64(str)}).plaintext
end

#decrypt_with_data_key(params) ⇒ String

Decrypt a blob using private keys

Parameters:

  • params (Hash)

Options Hash (params):

  • :cipher (String) —

    OpenSSL cipher used for encryption

  • :encrypted_key (String) —

    Encrypted private key

  • :encrypted_iv (String) —

    Encrypted initialization vector

  • :encrypted_data (String) —

    Ciphertext data blob

Returns:

  • (String) —

    Binary plaintext



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# File 'lib/kms-tools/decrypter.rb', line 22

def decrypt_with_data_key(params)
  cipher = OpenSSL::Cipher.new(params[:cipher])
  cipher.decrypt
  cipher.key = decrypt_string(params[:encrypted_key])
  cipher.iv = decrypt_string(params[:encrypted_iv])
  decrypted_data = cipher.update(params[:encrypted_data]) + cipher.final

  raise "File integrity check failed!" unless integrity_verified?(decrypted_data, params[:checksum])

  decrypted_data
end

#integrity_verified?(data, checksum) ⇒ Boolean

Verify data blob against known hash

Parameters:

  • data (String) —

    Data to verify

  • checksum (String) —

    Known SHA1 hash

Returns:

  • (Boolean) 


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# File 'lib/kms-tools/decrypter.rb', line 77

def integrity_verified?(data, checksum)
  Digest::SHA1.hexdigest(data).eql? checksum
end

#stream_decrypt_with_data_key(params) ⇒ Object

Decrypt a stream using private keys

Parameters:

  • params (Hash)

Options Hash (params):

  • :cipher (String) —

    OpenSSL cipher used for encryption

  • :encrypted_key (String) —

    Encrypted private key

  • :encrypted_iv (String) —

    Encrypted initialization vector

  • :in (Stream) —

    Input stream to read ciphertext data from

  • :position (Integer) —

    Optional file position marking beginning of ciphertext

  • :out (Stream) —

    Stream to to write plaintext output to

  • :checksum (String) —

    Optional SHA1 checksum to verify integrity of decrypted data



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# File 'lib/kms-tools/decrypter.rb', line 44

def stream_decrypt_with_data_key(params)
  # set up cipher
  cipher = OpenSSL::Cipher.new(params[:cipher])
  cipher.decrypt
  cipher.key = decrypt_string(params[:encrypted_key])
  cipher.iv = decrypt_string(params[:encrypted_iv])

  sha1 = Digest::SHA1.new if params[:checksum]

  # write the output stream
  chunk = ""
  params[:in].seek(params[:position], IO::SEEK_SET) if params[:position]
  while params[:in].read(STREAM_CHUNK_SIZE, chunk)
    decrypted_chunk = cipher.update(chunk)
    sha1.update(decrypted_chunk) if params[:checksum]
    params[:out] << decrypted_chunk
  end

  final = cipher.final
  sha1.update(final) if params[:checksum]

  if params[:checksum]
    raise "Decrypted data stream failed checksum verification!" unless params[:checksum].eql? sha1.hexdigest
  end

  params[:out] << final
  true
end