by Anish
Posted on Monday september 24, 2018
This sample chapter extracted from the book, Cryptography for JavaScript Developers.
The Web crypto api ECDSA algorithm identifier is used to perform signing and verification using the ECDSA algorithm specified in RFC6090 and using the SHA hash functions and elliptic curves defined in this specification.
This is the web cryptography api example of performing ecdsa message signing and verifying the signature
Generate ECDSA Keys using the named curved P-256, P-384, or P-521, The generated ECDSA keys is outputed in JWK format for demo purpose only
window.crypto.subtle.generateKey({
name: "ECDSA",
namedCurve: curve, //can be "P-256", "P-384", or "P-521"
},
true, //whether the key is extractable (i.e. can be used in exportKey)
["sign", "verify"] //can be any combination of "sign" and "verify"
)
.then(function(key) {
publicKey = key.publicKey;
privateKey = key.privateKey;
// For Demo Purpos Only Exported in JWK format
window.crypto.subtle.exportKey("jwk", key.publicKey).then(
function(keydata) {
publicKeyhold = keydata;
publicKeyJson = JSON.stringify(publicKeyhold);
document.getElementById("ecdsapublic").value = publicKeyJson;
}
);
window.crypto.subtle.exportKey("jwk", key.privateKey).then(
function(keydata) {
privateKeyhold = keydata;
privateKeyJson = JSON.stringify(privateKeyhold);
document.getElementById("ecdsaprivate").value = privateKeyJson;
}
);
ECDSA Sign the Message and generate signature
window.crypto.subtle.sign({
name: "ECDSA",
hash: {
name: "SHA-256"
}, //can be "SHA-1", "SHA-256", "SHA-384", or "SHA-512"
},
privateKey, //from generateKey or importKey above
asciiToUint8Array(plainText) //ArrayBuffer of data you want to sign
)
.then(function(signature) {
//returns an ArrayBuffer containing the signature
document.getElementById("cipherText").value = bytesToHexString(signature);
})
.catch(function(err) {
console.error(err);
});
})
.catch(function(err) {
console.error(err);
});
ECDSA Verify the message signature
window.crypto.subtle.verify({
name: "ECDSA",
hash: {name: "SHA-256"}, //can be "SHA-1", "SHA-256", "SHA-384", or "SHA-512"
},
publicKey, //from generateKey or importKey above
hexStringToUint8Array(cipherText), //ArrayBuffer of the data
asciiToUint8Array(plainText)
)
.then(function(decrypted) {
alert("Verified " + decrypted);
})
.catch(function(err) {
console.error(err);
});
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