ML-KEM Encapsulate

Category: Post-Quantum Cryptography · Node Type ID: pqc-mlkem-encaps

Encapsulates a shared key against recipient public key

Overview

Generates a fresh 32-byte (256-bit) post-quantum shared secret and encapsulates it against the recipient's ML-KEM public key (NIST FIPS 203), outputting both the 32-byte Shared Key (for the sender) and the encapsulated Ciphertext (to transmit to the recipient for decapsulation).

Ciphertext sizes are 768 bytes for ML-KEM-512, 1,088 bytes for ML-KEM-768, and 1,568 bytes for ML-KEM-1024.

When to Use

Establishing a 32-byte quantum-resistant symmetric session key with a recipient holding the corresponding ML-KEM secret key.

Parameter Configuration

Parameter (ID)	Type & Default	Visibility Condition	Description & Options
Variant `variant`	`select` Default: `768`	Always visible	Must match the ML-KEM security level of the connected `Recipient Public Key` (`512`, `768`, or `1024`). `512`: ML-KEM-512 `768`: ML-KEM-768 `1024`: ML-KEM-1024

Port I/O Specification

See Ports & Connections for general wiring rules, data type colors, and dynamic port creation.

Input Ports

Port Nature: Fixed Input Ports (1 total).

Port Name	Port ID	Data Type	Required	Visibility Condition	Description
`Recipient Public Key`	`publicKey`	`Bytes`	Required	Always visible	Recipient's ML-KEM encapsulation public key (800B, 1184B, or 1568B depending on variant).

Output Ports

Port Nature: Fixed Output Ports (2 total).

Port Name	Port ID	Data Type	Visibility Condition	Description
`Shared Key`	`sharedSecret`	`Bytes` (32B)	Always visible	Generated 32-byte shared secret key (ready for use with AES-256, ChaCha20-Poly1305, or HKDF).
`Ciphertext`	`ciphertext`	`Bytes`	Always visible	Encapsulated KEM ciphertext (768B, 1088B, or 1568B) to send to ML-KEM Decapsulate.

Error Cases

When any of the following conditions occurs at runtime, this node transitions to an ERROR state and downstream nodes connected to its outputs do not execute.

Error Code	Default Engine Message	Trigger Condition
`INVALID_KEY_MATERIAL`	Invalid key length or format	Raised when `Recipient Public Key` length does not match the selected ML-KEM variant or fails FIPS 203 modulus check.

Examples

Encapsulating a 32-Byte Key with ML-KEM-768

Encapsulate a shared key and encrypt a message with AES-256-GCM.

Connect Public Key from ML-KEM KeyGen to Recipient Public Key.
Connect Shared Key to the Key port of AES Encrypt, and send Ciphertext to ML-KEM Decapsulate.