JSS 4.5 Support for RSAPrivateKey.getModulus()

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Overview

In order to run Tomcat 8.5+ with SSL server certificate and key stored in HSM, the Tomcat HTTP NIO connector needs to be configured with PKCS #11 keystore with JSS as keystore provider. When Tomcat is configured this way, it will execute the following code in sun.security.KeyUtil to determine the size of the RSA key based on its modulus:

public static final int getKeySize(Key key) {
    ...
    } else if (key instanceof RSAKey) {
        RSAKey pubk = (RSAKey)key;
        size = pubk.getModulus().bitLength();
    ...
}

However, currently the RSAPrivateKey.getModulus() is not supported in JSS, so Tomcat will fail to start properly.

There are several ways to fix the problem.

Option 1: Get Modulus from Public Key

It may be possible to get the modulus of the public key corresponding to the private key. However, currently there seems to be no mechanism to get the public key directly from the private key.

Option 1a: Get Public Key from Certificate

Assuming there is a certificate that corresponds to the private key, it might be possible to implement a new CryptoManager.getCertFromPrivateKey() to get the certificate from the private key, then get the public key from the certificate, then get the modulus from the public key:

public class PK11RSAPrivateKey {

    public BigInteger getModulus() {

        CryptoManager cryptoManager = CryptoManager.getInstance();

        // get the certificate from the private key
        X509Certificate cert = cryptoManager.getCertFromPrivateKey(this);

        // get the public key from the certificate
        PublicKey publicKey = cert.getPublicKey();

        // return the modulus from the public key
        return publicKey.getModulus();
    }
}

Notes:

  • this option will not work if the certificate does not exist
  • it's not clear if CryptoManager.getCertFromPrivateKey() can be implemented efficiently (without looping through all existing certificates)

Option 1b: Get Public Key from Private Key

If the certificate cannot be guaranteed to exist, it might be possible to implement a new CryptoManager.getPublicKeyFromPrivateKey() to get the public key from the private key, then get the modulus from the public key:

public class PK11RSAPrivateKey {

    public BigInteger getModulus() {

        CryptoManager cryptoManager = CryptoManager.getInstance();

        // get the public key from the private key
        PublicKey publicKey = cryptoManager.getPublicKeyFromPrivateKey(this);

        // return the modulus from the public key
        return publicKey.getModulus();
    }
}

Notes:

  • this option does not depend on certificates
  • it's not clear if CryptoManager.getPublicKeyFromPrivateKey() can be implemented efficiently (without looping through all existing public keys)

Option 2: Get Modulus from Private Key

Option 2a: Using PK11_GetAttributes()

It might be possible to get the modulus of the private key directly using PK11_GetAttributes():

JNIEXPORT jbyteArray JNICALL
Java_org_mozilla_jss_pkcs11_PK11RSAPrivateKey_getModulusByteArray
    (JNIEnv *env, jobject this)
{
    // get private key
    JSS_PK11_getPrivKeyPtr(env, this, &privateKey);

    // get token of private key
    slot = PK11_GetSlotFromPrivateKey(privateKey);

    // login to token if necessary
    PK11_Authenticate(slot, PR_TRUE /*readCerts*/, NULL /*wincx*/);

    // get modulus from private key
    crv = PK11_GetAttributes(NULL, slot, privateKey->pkcs11ID, &theTemplate, 1);

    value = theTemplate.pValue;
    length = theTemplate.ulValueLen;

    // convert modulus into byte array

    return array;
}

Notes:

  • this option does not depend on certificates
  • currently PK11_GetAttributes() is available but not exported by NSS
  • this might be the most efficient solution

Option 2b: Using SECKEY_ConvertToPublicKey()

It might be possible to convert the private key into public key using SECKEY_ConvertToPublicKey() then get the modulus from the public key:

JNIEXPORT jbyteArray JNICALL
Java_org_mozilla_jss_pkcs11_PK11RSAPrivateKey_getModulusByteArray
    (JNIEnv *env, jobject this)
{
    // get private key
    JSS_PK11_getPrivKeyPtr(env, this, &privateKey);

    // get token of private key
    slot = PK11_GetSlotFromPrivateKey(privateKey);

    // login to token if necessary
    PK11_Authenticate(slot, PR_TRUE /*readCerts*/, NULL /*wincx*/);

    // convert private key into public key
    publicKey = SECKEY_ConvertToPublicKey(privateKey);

    // get modulus from public key
    value = publicKey->u.rsa.modulus.data;
    length = publicKey->u.rsa.modulus.len;

    // convert modulus into byte array

    return array;
}
  • this option does not require NSS changes

References