I have a DER-serialized private key. The tool I have to provide the key to gives me
algid parse error, not a sequence, and it looks like the problem is that the key is not PKCS#8.
The command that the most popular comment to the answer suggests, worked for me – I got a PKCS#8 key and the tool accepts it.
Now I am curious how can I find out whether the key is PKCS#1, PKCS#8 or something else?