Unprotected Headers

As well as the signed tokens, the encrypted tokens also have unprotected header. But with one difference: there are two unprotected headers:

• Shared unprotected header applicable to all recipients.

• Per-recipient unprotected header.

With the example below, we will create an encrypted token for two recipient and some unprotected header parameters:

$jwe = $jweBuilder
    ->create()
    ->withPayload('...')
    ->withSharedProtectedHeader(['enc' => 'A256GCM', 'alg' => 'A256KW'])
    ->withSharedHeader(['author' => 'John Doe'])
    ->addRecipient($recipient_public_key_1, ['message' => 'Hello World!'])
    ->addRecipient($recipient_public_key_2, ['description' => 'Nice song for you'])
    ->build();

The variable $jwe will be a valid JWE object built for two recipients. The unprotected header parameter author is applicable to the whole token while message and description are available only for the first and second recipient respectively.

Note: when an unprotected header is set, the Compact Serialization mode is not available.

Disjoint Header Parameters

RFC 7516 section 7.2.1 requires the header parameter names of the three locations to be disjoint: a given parameter must appear in exactly one of them. The builder refuses to produce such a token, and since 4.2 the JWEDecrypter refuses to read one.

Keep in mind that only the shared protected header is covered by the AAD:

• put alg, enc and anything a recipient must be able to trust in the shared protected header. alg and enc are never read from the shared unprotected header;

• keep the unprotected headers for the informational parameters, like the author, message and description of the example above.