keyring.ts

// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

import { EncryptedDataKey } from './encrypted_data_key'
import { immutableBaseClass, immutableClass } from './immutable_class'

import {
  isEncryptionMaterial,
  isDecryptionMaterial,
} from './cryptographic_material'
import {
  EncryptionMaterial,
  DecryptionMaterial,
  SupportedAlgorithmSuites,
} from './types'
import { needs } from './needs'
import { NodeAlgorithmSuite } from './node_algorithms'
import { WebCryptoAlgorithmSuite } from './web_crypto_algorithms'

/*
 * This public interface to the Keyring object is provided for
 * developers of CMMs and keyrings only. If you are a user of the AWS Encryption
 * SDK and you are not developing your own CMMs and/or keyrings, you do not
 * need to use it and you should not do so.
 */

export abstract class Keyring<S extends SupportedAlgorithmSuites> {
  async onEncrypt(
    material: EncryptionMaterial<S>
  ): Promise<EncryptionMaterial<S>> {
    /* Precondition: material must be a type of isEncryptionMaterial.
     * There are several security properties that NodeEncryptionMaterial and WebCryptoEncryptionMaterial
     * posses.
     * The unencryptedDataKey can only be written once.
     * If a data key has not already been generated, there must be no EDKs.
     * See cryptographic_materials.ts
     */
    needs(isEncryptionMaterial(material), 'Unsupported type of material.')

    const _material = await this._onEncrypt(material)

    /* Postcondition: The EncryptionMaterial objects must be the same.
     * See cryptographic_materials.ts.  The CryptographicMaterial objects
     * provide several security properties, including immutability of
     * the unencrypted data key and the ability to zero the data key.
     * This is insured by returning the same material.
     */
    needs(
      material === _material,
      'New EncryptionMaterial instances can not be created.'
    )

    /* Postcondition UNTESTED: If this keyring generated data key, it must be the right length.
     * See cryptographic_materials.ts This is handled in setUnencryptedDataKey
     * this condition is listed here to keep help keep track of important conditions
     */

    return material
  }

  abstract _onEncrypt(
    material: EncryptionMaterial<S>
  ): Promise<EncryptionMaterial<S>>

  /* NOTE: The order of EDK's passed to the onDecrypt function is a clear
   * intent on the part of the person who did the encryption.
   * The EDK's should always correspond to the order serialized.
   * It is the Keyrings responsibility to maintain this order.
   * The most clear example is from KMS.  KMS is a regional service.
   * This means that a call to decrypt an EDK must go to the
   * region that "owns" this EDK.  If the decryption is done
   * in a different region. To control this behavior the person
   * who called encrypt can control the order of EDK and in the
   * configuration of the KMS Keyring.
   */
  async onDecrypt(
    material: DecryptionMaterial<S>,
    encryptedDataKeys: EncryptedDataKey[]
  ): Promise<DecryptionMaterial<S>> {
    /* Precondition: material must be DecryptionMaterial. */
    needs(isDecryptionMaterial(material), 'Unsupported material type.')

    /* Precondition: Attempt to decrypt iif material does not have an unencrypted data key. */
    if (material.hasValidKey()) return material

    /* Precondition: encryptedDataKeys must all be EncryptedDataKey. */
    needs(
      encryptedDataKeys.every((edk) => edk instanceof EncryptedDataKey),
      'Unsupported EncryptedDataKey type'
    )

    const _material = await this._onDecrypt(material, encryptedDataKeys)

    /* Postcondition: The DecryptionMaterial objects must be the same.
     * See cryptographic_materials.ts.  The CryptographicMaterial objects
     * provide several security properties, including immutability of
     * the unencrypted data key and the ability to zero the data key.
     * This is insured by returning the same material.
     */
    needs(
      material === _material,
      'New DecryptionMaterial instances can not be created.'
    )

    /* See cryptographic_materials.ts The length condition is handled there.
     * But the condition is important and so repeated here.
     * The postcondition is "If an EDK was decrypted, its length must agree with algorithm specification."
     * If this is not the case, it either means ciphertext was tampered
     * with or the keyring implementation is not setting the length properly.
     */

    return material
  }

  abstract _onDecrypt(
    material: DecryptionMaterial<S>,
    encryptedDataKeys: EncryptedDataKey[]
  ): Promise<DecryptionMaterial<S>>
}

immutableBaseClass(Keyring)

export abstract class KeyringNode extends Keyring<NodeAlgorithmSuite> {}
immutableClass(KeyringNode)
export abstract class KeyringWebCrypto extends Keyring<WebCryptoAlgorithmSuite> {}
immutableClass(KeyringWebCrypto)