Class: Aws::S3::Encryption::KmsCipherProvider Private

Inherits:
Object
  • Object
show all
Defined in:
lib/aws-sdk-s3/encryption/kms_cipher_provider.rb

This class is part of a private API. You should avoid using this class if possible, as it may be removed or be changed in the future.

Instance Method Summary collapse

Constructor Details

#initialize(options = {}) ⇒ KmsCipherProvider

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Returns a new instance of KmsCipherProvider.


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# File 'lib/aws-sdk-s3/encryption/kms_cipher_provider.rb', line 11

def initialize(options = {})
  @kms_key_id = options[:kms_key_id]
  @kms_client = options[:kms_client]
end

Instance Method Details

#decryption_cipher(envelope, options = {}) ⇒ Cipher

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Returns Given an encryption envelope, returns a decryption cipher.

Returns:

  • (Cipher)

    Given an encryption envelope, returns a decryption cipher.


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# File 'lib/aws-sdk-s3/encryption/kms_cipher_provider.rb', line 39

def decryption_cipher(envelope, options = {})
  encryption_context = Json.load(envelope['x-amz-matdesc'])
  cek_alg = envelope['x-amz-cek-alg']

  case envelope['x-amz-wrap-alg']
  when 'kms'; # NO OP
  when 'kms+context'
    if cek_alg != encryption_context['aws:x-amz-cek-alg']
      raise Errors::DecryptionError, 'Value of cek-alg from envelope'\
      ' does not match the value in the encryption context'
    end
  when 'AES/GCM'
    raise ArgumentError, 'Key mismatch - Client is configured' \
            ' with a KMS key and the x-amz-wrap-alg is AES/GCM.'
  when 'RSA-OAEP-SHA1'
    raise ArgumentError, 'Key mismatch - Client is configured' \
            ' with a KMS key and the x-amz-wrap-alg is RSA-OAEP-SHA1.'
  else
    raise ArgumentError, 'Unsupported wrap-alg: ' \
        "#{envelope['x-amz-wrap-alg']}"
  end

  key = @kms_client.decrypt(
    ciphertext_blob: decode64(envelope['x-amz-key-v2']),
    encryption_context: encryption_context
  ).plaintext

  iv = decode64(envelope['x-amz-iv'])
  block_mode =
    case cek_alg
    when 'AES/CBC/PKCS5Padding'
      :CBC
    when 'AES/CBC/PKCS7Padding'
      :CBC
    when 'AES/GCM/NoPadding'
      :GCM
    else
      type = envelope['x-amz-cek-alg'].inspect
      msg = "unsupported content encrypting key (cek) format: #{type}"
      raise Errors::DecryptionError, msg
    end
  Utils.aes_decryption_cipher(block_mode, key, iv)
end

#encryption_cipherArray<Hash,Cipher>

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Returns Creates an returns a new encryption envelope and encryption cipher.

Returns:

  • (Array<Hash,Cipher>)

    Creates an returns a new encryption envelope and encryption cipher.


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# File 'lib/aws-sdk-s3/encryption/kms_cipher_provider.rb', line 18

def encryption_cipher
  encryption_context = { "kms_cmk_id" => @kms_key_id }
  key_data = @kms_client.generate_data_key(
    key_id: @kms_key_id,
    encryption_context: encryption_context,
    key_spec: 'AES_256',
  )
  cipher = Utils.aes_encryption_cipher(:CBC)
  cipher.key = key_data.plaintext
  envelope = {
    'x-amz-key-v2' => encode64(key_data.ciphertext_blob),
    'x-amz-iv' => encode64(cipher.iv = cipher.random_iv),
    'x-amz-cek-alg' => 'AES/CBC/PKCS5Padding',
    'x-amz-wrap-alg' => 'kms',
    'x-amz-matdesc' => Json.dump(encryption_context)
  }
  [envelope, cipher]
end