I have a BTC wallet backup copy in PKCS1 private key format. Sadly, my friend created the wallet for me and I didn't take part in creating it. And I don't know on what platform was it created.To sum up, I have an address of my BTC wallet and this back up file. The content of which I changed for the example. Maybe there is some way to extract the key using Python or Terminal. Thanks!
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
I did a lot of googling and I didn't find the answer if Bitcoin Private Key can contain PKCS1 private key.