fix: BYTES_PER_KEY value (#193)

Maximum number of bytes that are allowed to be encrypted
under a single cached data key across messages.
The maximum value defined in the AWS Encryption SDK specification is 2 ** 63 - 1.
However Javascript can only perform safe operations on values
up to Number.MAX_SAFE_INTEGER === 9007199254740991 === 2 ** 53 - 1.
e.g
Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2 => true
Number.MAX_SAFE_INTEGER + 1 > Number.MAX_SAFE_INTEGER + 2 => false
Number.MAX_SAFE_INTEGER + 1 < Number.MAX_SAFE_INTEGER + 2 => false

This means that after 2 ** 53 - 1 the process of accumulating a byte count
will never yield an accurate comparison and so, never halt.

The choice here to use 2 ** 53 - 1 instead of Number.MAX_SAFE_INTEGER is deliberate.
This is because in the future Number.MAX_SAFE_INTEGER could be raised to 2 ** 66
or some value larger 2 ** 63.

Author: seebees

modules/cache-material/src/caching_cryptographic_materials_decorators.ts

@@ -49,17 +49,17 @@ export function decorateProperties<S extends SupportedAlgorithmSuites> (
   /* Precondition: You *can not* cache something forever. */
   needs(maxAge > 0, 'You must configure a maxAge')
   /* Precondition: maxBytesEncrypted must be inside bounds.  i.e. positive and not more than the maximum. */
-  needs(!maxBytesEncrypted || (maxBytesEncrypted > 0 && Maximum.BYTES_PER_KEY >= maxBytesEncrypted), 'maxBytesEncrypted is outside of bounds.')
+  needs(!maxBytesEncrypted || (maxBytesEncrypted > 0 && Maximum.BYTES_PER_CACHED_KEY_LIMIT >= maxBytesEncrypted), 'maxBytesEncrypted is outside of bounds.')
   /* Precondition: maxMessagesEncrypted must be inside bounds.  i.e. positive and not more than the maximum. */
-  needs(!maxMessagesEncrypted || (maxMessagesEncrypted > 0 && Maximum.MESSAGES_PER_KEY >= maxMessagesEncrypted), 'maxMessagesEncrypted is outside of bounds.')
+  needs(!maxMessagesEncrypted || (maxMessagesEncrypted > 0 && Maximum.MESSAGES_PER_CACHED_KEY_LIMIT >= maxMessagesEncrypted), 'maxMessagesEncrypted is outside of bounds.')
   /* Precondition: partition must be a string. */
   needs(partition && typeof partition === 'string', 'partition must be a string.')
 
   readOnlyProperty(obj, '_cache', cache)
   readOnlyProperty(obj, '_backingMaterialsManager', backingMaterialsManager)
   readOnlyProperty(obj, '_maxAge', maxAge)
-  readOnlyProperty(obj, '_maxBytesEncrypted', maxBytesEncrypted || Maximum.BYTES_PER_KEY)
-  readOnlyProperty(obj, '_maxMessagesEncrypted', maxMessagesEncrypted || Maximum.MESSAGES_PER_KEY)
+  readOnlyProperty(obj, '_maxBytesEncrypted', maxBytesEncrypted || Maximum.BYTES_PER_CACHED_KEY_LIMIT)
+  readOnlyProperty(obj, '_maxMessagesEncrypted', maxMessagesEncrypted || Maximum.MESSAGES_PER_CACHED_KEY_LIMIT)
   readOnlyProperty(obj, '_partition', partition)
 }
 

modules/serialize/src/identifiers.ts

@@ -61,9 +61,25 @@ Object.freeze(SequenceIdentifier)
 
 export enum Maximum {
   // Maximum number of messages which are allowed to be encrypted under a single cached data key
-  MESSAGES_PER_KEY = 2 ** 32, // eslint-disable-line no-unused-vars
-  // Maximum number of bytes which are allowed to be encrypted under a single cached data key
-  BYTES_PER_KEY = 2 ** 63 - 1, // eslint-disable-line no-unused-vars
+  MESSAGES_PER_CACHED_KEY_LIMIT = 2 ** 32, // eslint-disable-line no-unused-vars
+  /* Maximum number of bytes that are allowed to be encrypted
+   * under a single cached data key across messages.
+   * The maximum value defined in the AWS Encryption SDK specification is 2 ** 63 - 1.
+   * However Javascript can only perform safe operations on values
+   * up to Number.MAX_SAFE_INTEGER === 9007199254740991 === 2 ** 53 - 1.
+   * e.g
+   * Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2 => true
+   * Number.MAX_SAFE_INTEGER + 1 > Number.MAX_SAFE_INTEGER + 2 => false
+   * Number.MAX_SAFE_INTEGER + 1 < Number.MAX_SAFE_INTEGER + 2 => false
+   *
+   * This means that after 2 ** 53 - 1 the process of accumulating a byte count
+   * will never yield an accurate comparison and so, never halt.
+   *
+   * The choice here to use 2 ** 53 - 1 instead of Number.MAX_SAFE_INTEGER is deliberate.
+   * This is because in the future Number.MAX_SAFE_INTEGER could be raised to 2 ** 66
+   * or some value larger 2 ** 63.
+   */
+  BYTES_PER_CACHED_KEY_LIMIT = 2 ** 53 - 1, // eslint-disable-line no-unused-vars
   // Maximum number of frames allowed in one message as defined in specification
   FRAME_COUNT = 2 ** 32 - 1, // eslint-disable-line no-unused-vars
   // Maximum bytes allowed in a single frame as defined in specification