Regular Expression to detect private and public RSA keys - regex

Question

I've searched over the internet but with no results,
There is any pattern (to be implemented in regex) to detect RSA private or public keys ?
(not included strings such as ---- Public RSA key-- or "ssh rsa")
I'm stuck after create base64 regex
var re = regexp.MustCompile(`(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3})=`)
Thanks

Answer 1

Get pem formatted block
If your document contains not only PEM formatted block than Decode function from encoding/pem package will be helpful:
Decode will find the next PEM formatted block (certificate, private key etc) in the input. It returns that block and the remainder of the input. If no PEM data is found, p is nil and the whole of the input is returned in rest.
Parse key and check for rsa conformity
Go contains package named crypto to do such things like parsing keys and certifies. For purpose of parsing public keys provided function ParsePKIXPublicKey:
Supported key types include RSA, DSA, and ECDSA. Unknown key types result in an error.
On success, pub will be of type *rsa.PublicKey, *dsa.PublicKey, or *ecdsa.PublicKey.
On return you obtain concrete type which is easy to assert with type switch (idiomatic way to determine type of variable):
Example:
// There is a key
const pubPEM = `MIICIjANBgkqhkiG9...`
// Ignore the rest of document
block, _ := pem.Decode([]byte(pubPEM))
if block == nil {
log.Fatal("The document doesn't contain PEM blocks.")
}
pub, err := x509.ParsePKIXPublicKey(block.Bytes)
if err != nil {
log.Fatal("The block is not a DER encoded public key.")
}
switch pub := pub.(type) {
case *rsa.PublicKey:
fmt.Println("pub is of type RSA:", pub)
default:
log.Fatal("The key is not RSA encripted.")
}