public string CheckPrivateKey(string key)
{
if (!b58End.HasValidChars(key))
{
return("The given key contains invalid base-58 characters.");
}
if (!b58End.HasValidCheckSum(key))
{
return("The given key has an invalid checksum.");
}
byte[] keyBa = b58End.DecodeWithCheckSum(key);
if (keyBa[0] != Constants.PrivKeyFirstByte)
{
return($"Invalid first key byte (actual={keyBa[0]}, expected={Constants.PrivKeyFirstByte}).");
}
if (keyBa.Length == 33)
{
if (!IsPrivateKeyInRange(keyBa.SubArray(1)))
{
return("Invalid key integer value (outside of the range defined by secp256k1 curve).");
}
return("The given key is a valid uncompressed private key.");
}
else if (keyBa.Length == 34)
{
if (keyBa[^ 1] != Constants.PrivKeyCompLastByte)
