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CoseAgent.md

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CoseAgent documentation

Module to build COSE message agents (signers, recipients and counter signers).

Properties

Name Type Getter Setter Description
header CoseHeader Yes Yes COSE header object.
payload Uint8Array Yes No Payload of the agent object (ciphertext or signature).

When decoding a COSE message, after the function init_decoding, all the COSE message parameters will be accessible by the previously listed getters.

Methods

Name Parameters Returns Description
key(key: CoseKey) key: COSE key. --- Sets the COSE key to be used.
ephemeral_key(key: CoseKey, prot: bool, crit: bool) key: COSE ephemeral key.
prot: If its to be included in protected header.
crit: If its to be included in crit COSE array.		 --- Sets the COSE ephemeral key for Direct Key Agreement.
static_key(key: CoseKey, prot: bool, crit: bool) key: COSE static key.
prot: If to be included in protected header.
crit: If its to be included in crit COSE array.		 --- Sets the COSE static key for Direct Key Agreement.
static_kid(kid: Uint8Array, key: CoseKey, prot: bool, crit: bool) kid: Static Key ID.
key: COSE static key.
prot: If to be included in protected header.
crit: If its to be included in crit COSE array.		 --- Sets the COSE static key for Direct Key Agreement, including only the Key ID on the final COSE message.
add_signature(signature: Uint8Array) signature: COSE signature. --- Sets the Counter Signature (Method to be used when the counter signature is produced externally.

Examples

Examples with recipients/signers can be found in each COSE message type Module.

Counter signers

Counter signature in cose-sign1 message.

Encode

var {
  CoseKey,
  CoseMessage,
  CoseHeader,
  CoseAgent,
  Alg,
  Kty,
  Crv,
  KeyOp
} = require('cose-w');

let msg = Buffer.from('546869732069732074686520636F6E74656E742E', 'hex');

// Prepare signer cose-key
let key1 = new CoseKey();
key1.kty = Kty.ec2;
key1.alg = Alg.es256;
key1.crv = Crv.p_256;
key1.d = Buffer.from('57c92077664146e876760c9520d054aa93c3afb04e306705db6090308507b4d3', 'hex');
key1.key_ops = [KeyOp.sign];

// Prepare counter signer cose-key
let key2 = new CoseKey();
key2.kty = Kty.ec2;
key2.alg = Alg.es256;
key2.crv = Crv.p_256;
key2.d = Buffer.from('57c92077664146e876760c9520d054aa93c3afb04e306705db6090308507b4d3', 'hex');
key2.key_ops = [KeyOp.sign];


// Prepare CoseSign
let sign = CoseMessage.new_sign();
sign.payload = msg;
let header = new CoseHeader();
header.set_alg(Alg.es256, true, false);
header.set_kid([1], true, false);
sign.header = header;
sign.key(key1);

// Generate signature
sign.secure_content(null);

// Prepare counter signer
let counter1 = CoseAgent.new_counter_sig();
header = new CoseHeader();
header.set_kid([0], true, false);
header.set_alg(Alg.es256, true, false);
counter1.header = header;
counter1.key(key1);

// Add counter signature to cose-sign1
sign.counter_sig(null, counter1);
sign.add_counter_sig(counter1);

// Encode the cose-sign1 message
let bytes = sign.encode(true);

Decode

var {
  CoseKey,
  CoseMessage,
  Alg,
  Kty,
  Crv,
  KeyOp
} = require('cose-w');

// Prepare signer cose-key
let key1 = new CoseKey();
key1.kty = Kty.ec2;
key1.alg = Alg.es256;
key1.crv = Crv.p_256;
key1.x = Buffer.from('bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', 'hex');
key1.y = Buffer.from('20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e', 'hex');
key1.key_ops = [KeyOp.verify];

// Prepare counter signer cose-key
let key2 = new CoseKey();
key2.kty = Kty.ec2;
key2.alg = Alg.es256;
key2.crv = Crv.p_256;
key2.x = Buffer.from('bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', 'hex');
key2.y = Buffer.from('20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e', 'hex');
key2.key_ops = [KeyOp.verify];

// Prepare CoseSign with the cose-sign1 bytes
let verify = CoseMessage.new_sign();
verify.bytes = Buffer.from("d28446a20126044101a1078346a20441000126a05840b94eb54af9aba9250c3aabf65c7da5583d0c1b4e813f9dead8b5ac0fbc3afa2ae57ae88905c80f100771394501bc447d6064afcbdf88bb0620863f1e0827406554546869732069732074686520636f6e74656e742e5840cf6f9dd76e5c7252e72bf6bf685fced5d82309c4ae0df229a501529636106ae99ddb5efc8b73c208ddbc815f91d71dc9b7db8ce6390f76ad01ba256fc0eae575", "hex");

// Init decoding
verify.init_decoder(null);

// Add key and verify signature
verify.key(key1);
let payload = verify.decode(null, null);

// Get counter signer and verify counter signature
let i = verify.counter([0]);
verify.set_counter_key(i, null, key1);
verify.counters_verify(null, i, null);