Encode Private Key getting Error: asn1: structure error: tags don't match

Question

When i try to parses the encode private key with

sample private key

-----BEGIN OPENSSH PRIVATE KEY-----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-----END OPENSSH PRIVATE KEY-----

 x509.ParsePKCS1PrivateKey(block.Bytes)

it will giving me error Explain:

case "OPENSSH PRIVATE KEY":
        log.Println("Here at OPENSSH Private Key:")
        rsa, err := x509.ParsePKCS1PrivateKey(block.Bytes)
        log.Println("Rsa and Error:", rsa, err)
        if err != nil {
            return nil, err
        }
        rawkey = rsa

key

-----BEGIN OPENSSH PRIVATE KEY-----
key
-----END OPENSSH PRIVATE KEY-----

Getting Error:

asn1: structure error: tags don't match (16 vs {class:1 tag:15 length:112 isCompound:true}) {optional:false explicit:false application:false private:false defaultValue:<nil> tag:<nil> stringType:0 timeType:0 set:false omitEmpty:false} pkcs1PrivateKey @2
2019/04/02 13:57:52 Signer: <nil>

and I will also try with

 x509.ParsePKCS8PrivateKey(block.Bytes)

But same Error getting.

Answer 1

The problem is the key type. OPENSSH PRIVATE KEY should be parsed with ssh.ParseRawPrivateKey, whereas RSA PRIVATE KEY can be parsed with both ssh.ParseRawPrivateKey and x509.ParsePKCS1PrivateKey.

You can generate RSA PRIVATE KEY with e.g. ssh-keygen -t rsa -f key.pem -m pem (-m pem here is important) or openssl genrsa -out key.pem, and test it with openssl rsa -check -in key.pem.

So just do a block type check and use the corresponding functions in the case clauses to parse the key.

Also think about key encryption, which means you might need to use ssh.ParseRawPrivateKeyWithPassphrase or x509.IsEncryptedPEMBlock and x509.DecryptPEMBlock functions too.