How to convert 65 bytes 88 characters base64 string to 124 characters and vice versa?

[chlin501]

I use following Java 11 code to produce a public key. And I notice that the base64 encoding's public key length is 124 characters.

    KeyPairGenerator generator = KeyPairGenerator.getInstance("EC");
    ECGenParameterSpec spec = new ECGenParameterSpec("secp256r1");
    generator.initialize(spec);
    KeyPair pair = generator.genKeyPair();
    PublicKey pubKey = pair.getPublic();
    String byte65_124chars = Base64.getEncoder().toBase64String(pubKey.getEncoded());
    System.out.println("pub key base64 encoding: "+byte65_124chars);

I found some info. It looks like it is because 124 characters contains some more info. So I attempted to generate 88 characters using Bouncy Castle ASN1Primitive.

   ASN1Primitive p;
    while ((p = input.readObject()) != null) {
        System.out.println(ASN1Dump.dumpAsString(p, true));
    }

But the output as follow doesn't contain any 88 characters string I am looking for. It seems to me the last 3 line are what I after, but I do not find corresponded conversion methods.

Sequence
    Sequence
        ObjectIdentifier(1.2.840.10045.2.1)
        ObjectIdentifier(1.2.840.10045.3.1.7)
    DER Bit String[65, 0] 
        046b89ae9a8f38f5651982e4550480cd2c9affe70998faeace6ac6fcd14d4e46    k8eU,jMNF
        1f35ad7536aec9864b5ced0b1eeade2792f60ada04b3deea58c97923f2612597    5u6K\'Xy#a%
        45      

Using ASN1UniversalString, at runtime it throws encoding error getInstance: java.lang.IllegalStateException: unexpected object: org.bouncycastle.asn1.DLSequence. What is the right way to convert the 88 characters public key from and to 124 characters, and vice versa?

    ASN1UniversalString str = ASN1UniversalString.getInstance(input.readAllBytes());
    System.out.println(str.getString());

Many thanks.