Verified boot keystore generateion failure

Question

I need to generate my own keystore for Android Verified Boot. I took these steps

1. mmma system/extra/verity
2. keystore_signer private.der verity.x509.pem keystore.img verity.der

And i got this error

Exception in thread "main" java.lang.IllegalArgumentException: unknown object in getInstance: org.bouncycastle.asn1.ASN1Integer
    at org.bouncycastle.asn1.ASN1Sequence.getInstance(ASN1Sequence.java:98)
    at org.bouncycastle.asn1.x509.AlgorithmIdentifier.getInstance(AlgorithmIdentifier.java:47)
    at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.<init>(PrivateKeyInfo.java:85)
    at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.getInstance(PrivateKeyInfo.java:45)
    at com.android.verity.Utils.loadDERPrivateKey(Utils.java:173)
    at com.android.verity.Utils.loadDERPrivateKeyFromFile(Utils.java:189)
    at com.android.verity.BootKeystore.main(KeystoreSigner.java:203)

It seems that keystore_signer failed to load private.der. but i can't find where i did wrong