COSEEncrypt

COSEEncrypt refers to the COSE_Encrypt message type defined in RFC 8152, part of the COSE (CBOR Object Signing and Encryption) family. It is used to encrypt content for one or more recipients, providing confidentiality and integrity protection through authenticated encryption.

Structure and key concepts: A COSE_Encrypt message is encoded in CBOR and consists of an overall ciphertext along with header information and recipient-specific data. The message includes a protected header (a CBOR-encoded map, often containing algorithm identifiers such as the content encryption algorithm and key management method), an unprotected header (a non-protected map with additional parameters), and the ciphertext. In addition, there is a recipients array, where each recipient entry holds per-recipient header information and the data necessary to derive or transport the content encryption key for that recipient (for example, an encrypted key or key agreement material). The content encryption key (CEK) is used to encrypt the actual payload, and per-recipient processing ensures that each recipient can obtain the CEK using their own key material.

Usage and capabilities: COSE_Encrypt enables secure distribution of encrypted content to multiple recipients, potentially with different cryptographic algorithms per recipient. It supports various key management methods (e.g., direct symmetric keys, RSA-based methods, or elliptic-curve key agreement) and allows for per-recipient flexibility while maintaining a single ciphertext. Compared to COSE_Encrypt0, COSE_Encrypt handles multiple recipients and their corresponding key transport mechanisms.

Applications: The format is suitable for resource-constrained environments, such as Internet of Things deployments, where secure, multicast-like or multi-recipient content delivery is needed with robust integrity and confidentiality guarantees.