anchor.diff:  * http://tools.ietf.org/html/draft-ietf-jose-json-web-encryption-40
   * http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-40
   * http://tools.ietf.org/html/draft-mcgrew-aead-aes-cbc-hmac-sha2-05
  +* http://tools.ietf.org/html/rfc3394
   
   
   [[jws]]
  
positive.code: 
  
  === Claims validation
  
  
  _buddy-sign_ json web encryption, like *jws*, also implements validation of a concrete subset
  of claims related to the age of the signed data: *exp* (expiration time), *nbf* (not before).
  
negative.code: and content encryption algorithms.
  
  The *key encryption algorithms* are responsible of encrypt the key that will be used for encrypt the
  content. This is a table that exposes the currently supported _Key Encryption Algorithms_ (specified
  in JWA RFC):
  
  .Supported Key Encryption Algorithms
  [options="header", cols="1,2,1,1"]
  |===================================================================================
  | Algorithm name | Decription | Keyword       | Shared Key Size
  | DIR            | Direct use of a shared symmetric key | `:dir` | (depends on content
  encryption algorithm)
  | A128KW         | AES128 Key Wrap | `:a128kw`    | 16 bytes
  | A192KW         | AES192 Key Wrap | `:a192kw`    | 24 bytes
  | A256KW         | AES256 Key Wrap | `:a256kw`    | 32 bytes
  |===================================================================================
  
  
  The *conentent encryption algoritms* are responsible of encrypt the content. This is a table
  that exposes the currently supported _Content Encryption Algorithms_ (all specified
  in the JWA RFC):
  
  .Supported Content Encryption Algorithms
  [options="header", cols="1,1,1,1"]
  |===================================================================================
  | Algorithm name | Description | Keyword | Shared Key Size
  | A128CBC-HS256  | AES128 with CBC mode and HMAC-SHA256  | `:a128-hs256` | 32 bytes
  | A192CBC-HS384  | AES192 with CBC mode and HMAC-SHA384  | `:a192-hs384` | 48 bytes
  | A256CBC-HS512  | AES256 with CBC mode and HMAC-SHA512  | `:a256-hs512` | 64 bytes
  | A128GCM        | AES128 with GCM mode | `:a128gcm`    | 16 bytes
  | A192GCM        | AES192 with GCM mode | `:a192gcm`    | 24 bytes
  | A256GCM        | AES256 with GCM mode | `:a256gcm`    | 32 bytes
  |===================================================================================
  
  
  