What is JSON Web Encryption (JWE)?
As defined in the RFC 7516, JSON Web Encryption (JWE) is a mechanism to encrypt and decrypt data in JSON format. It adds a layer of confidentiality to the data, and is practicularly useful when transmitting sensitive information over an untrusted network.
JWE is often used in conjunction with JSON Web Tokens (JWTs) to protect the payload data. For example, an ID token or Access token can be encrypted using JWE to ensure that the data is secure during transmission.
How does JWE work?
JWE has two serialization formats: compact and JSON. Each format has its own way of representing the encrypted data.
Compact serialization
In the compact serialization, the JWE is represented as a string with five Base64URL-encoded parts separated by dots (.). The five parts are:
{{header}}.{{encrypted-key}}.{{iv}}.{{ciphertext}}.{{tag}}
Each part has a specific purpose:
header: Contains metadata about the encryption algorithm and key management.encrypted-key: The encrypted content encryption key (CEK) used to encrypt the payload.iv: The initialization vector used in the encryption process.ciphertext: The encrypted payload data.tag: The authentication tag used to verify the integrity of the encrypted data.
JSON serialization
JSON serialization is more verbose and provides a structured way to represent the JWE. The JWE is represented as a JSON object with the following properties:
{
"protected": "{{protected-header}}",
"unprotected": "{{unprotected-header}}",
"header": "{{header}}",
"encrypted_key": "{{encrypted-key}}",
"iv": "{{iv}}",
"ciphertext": "{{ciphertext}}",
"tag": "{{tag}}",
"aad": "{{additional-authenticated-data}}"
}
protected: Contains the Base64URL-encoded protected header.unprotected: Contains JWE shared unprotected header.header: Contains the JWE per-recipient unprotected header.encrypted_key: Contains the encrypted content encryption key (CEK) that is Base64URL-encoded.iv: Contains the Base64URL-encoded initialization vector.ciphertext: Contains the Base64URL-encoded ciphertext (encrypted payload).tag: Contains the Base64URL-encoded authentication tag.aad: Contains the Base64URL-encoded additional authenticated data.
The client should be able to decrypt the JWE using the appropriate key and algorithm. A pre-communiated key or a key derived from a key agreement protocol can be used to decrypt the JWE.
For example, an ID token may be encrypted using JWE, and the client can decrypt it using the appropriate key obtained from the jwks_uri endpoint of the OpenID provider.