TextSecure Signal Server - Certificate Error

I was trying to deploy Signal Server according to the guidelines here.
Link

Everything was success in the build part. But when i run the service using this command

java -jar service/target/TextSecureServer-3.21.jar server service/config/config.yml

I am getting below errors.

INFO  [2020-09-10 04:52:48,319] io.dropwizard.server.DefaultServerFactory: Registering jersey handler with root path prefix: /
INFO  [2020-09-10 04:52:48,320] io.dropwizard.server.DefaultServerFactory: Registering admin handler with root path prefix: /
org.bouncycastle.openssl.PEMException: problem parsing cert: java.security.cert.CertificateException: java.lang.IllegalArgumentException: unknown object in factory: org.bouncycastle.asn1.DERUnknownTag
	at org.bouncycastle.openssl.PEMReader$X509CertificateParser.parseObject(Unknown Source)
	at org.bouncycastle.openssl.PEMReader.readObject(Unknown Source)
	at org.whispersystems.textsecuregcm.push.RetryingApnsClient.initializeCertificate(RetryingApnsClient.java:76)
	at org.whispersystems.textsecuregcm.push.RetryingApnsClient.<init>(RetryingApnsClient.java:49)
	at org.whispersystems.textsecuregcm.push.APNSender.<init>(APNSender.java:70)
	at org.whispersystems.textsecuregcm.WhisperServerService.run(WhisperServerService.java:246)
	at org.whispersystems.textsecuregcm.WhisperServerService.run(WhisperServerService.java:151)
	at io.dropwizard.cli.EnvironmentCommand.run(EnvironmentCommand.java:44)
	at io.dropwizard.cli.ConfiguredCommand.run(ConfiguredCommand.java:87)
	at io.dropwizard.cli.Cli.run(Cli.java:78)
	at io.dropwizard.Application.run(Application.java:94)
	at org.whispersystems.textsecuregcm.WhisperServerService.main(WhisperServerService.java:406)
Caused by: java.security.cert.CertificateException: java.lang.IllegalArgumentException: unknown object in factory: org.bouncycastle.asn1.DERUnknownTag
	at org.bouncycastle.jce.provider.JDKX509CertificateFactory.engineGenerateCertificate(Unknown Source)
	at java.base/java.security.cert.CertificateFactory.generateCertificate(CertificateFactory.java:355)
	... 12 more
Caused by: java.lang.IllegalArgumentException: unknown object in factory: org.bouncycastle.asn1.DERUnknownTag
	at org.bouncycastle.asn1.x509.AlgorithmIdentifier.getInstance(Unknown Source)
	at org.bouncycastle.asn1.x509.TBSCertificateStructure.<init>(Unknown Source)
	at org.bouncycastle.asn1.x509.TBSCertificateStructure.getInstance(Unknown Source)
	at org.bouncycastle.asn1.x509.X509CertificateStructure.<init>(Unknown Source)
	at org.bouncycastle.asn1.x509.X509CertificateStructure.getInstance(Unknown Source)
	at org.bouncycastle.jce.provider.JDKX509CertificateFactory.readDERCertificate(Unknown Source)
	... 14 more

Anyone know the exact issue here ?

Also i didnt change serverSecret & serverPublic under zkConfig. (I dont know how to get these). What it does mean by * # zkgroup config, run using your build jar * as in the documentation ?

Problem solved. This exception came due to improper PEM format of reading cerKey file. Anyhow current crtKey form is PEM only, but it need a extended form of PEM.

i used below command to generate it.

openssl rsa -in cert.key -outform PEM -out cert.key   

Then all above errors were disappeared.

I did enter the above command but i got this error

> Can't open cert.key for reading, No such file or directory
140021811573184:error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:72:fopen('cert.key','r')
140021811573184:error:2006D080:BIO routines:BIO_new_file:no such file:../crypto/bio/bss_file.c:79:
unable to load Private Key

and I did everything I could I generated all kind of certificate I could find on Internet but no change in result. could you please tell me what to do it's so important to me. thanks alot