Convert privateKey to PKCS#8 format in Dart

Question

In FLUTTER - DART using RSA algoritm i get a privateKey. I have this method for encode privateKey to PEM in PKCS#1 format but i need a method for encode the privateKey to PKCS#8 format. I can't finde nothing in internet for that.

Uint8List _encodePrivateKeyToPemPKCS1(RSAPrivateKey privateKey) {
    var topLevel = new ASN1Sequence();

    var version = ASN1Integer(BigInt.from(0));
    var modulus = ASN1Integer(privateKey.n!);
    var publicExponent = ASN1Integer(privateKey.exponent!);
    var privateExponent = ASN1Integer(privateKey.privateExponent!);
    var p = ASN1Integer(privateKey.p!);
    var q = ASN1Integer(privateKey.q!);
    var dP = privateKey.privateExponent! % (privateKey.p! - BigInt.from(1));
    var exp1 = ASN1Integer(dP);
    var dQ = privateKey.privateExponent! % (privateKey.q! - BigInt.from(1));
    var exp2 = ASN1Integer(dQ);
    var iQ = privateKey.q!.modInverse(privateKey.p!);
    var co = ASN1Integer(iQ);

    topLevel.add(version);
    topLevel.add(modulus);
    topLevel.add(publicExponent);
    topLevel.add(privateExponent);
    topLevel.add(p);
    topLevel.add(q);
    topLevel.add(exp1);
    topLevel.add(exp2);
    topLevel.add(co);

    return topLevel.encodedBytes;
}

Solution

This code work for me. Thanks Topaco

https://raw.githubusercontent.com/Ephenodrom/Dart-Basic-Utils/master/lib/src/CryptoUtils.dart

https://raw.githubusercontent.com/Ephenodrom/Dart-Basic-Utils/master/lib/src/StringUtils.dart

Comments

[Topaco]

This code generates a PEM encoded private key in PKCS#8 from an RSAPrivateKey object. Not tested, so you should check the generated key, e.g. with openssl rsa -check.

[Maarten Bodewes]

Please indicate if it has worked or not, you can answer your own question if it does.

[Topaco]

For newer PointyCastle versions, see these links to the updated code: gist.github.com/proteye/…, in particular CryptoUtils.encodeRSAPrivateKeyToPem()