Secret Key
Secret key cryptography relies on using the same key to encode and then later decode a message. Thus, only those who know the “secret” can read the message. RSA security is based on 2 matching keys. There is a public key for each user, and everybody can (should) know it. There is also a private key that only the user should know. A message encrypted by the public key can only be decrypted by the private key, and visa versa. Thus, if I want to send you a message that only you can read, I get (from the network) your public key, encrypt the message with that key and you are the only person who can decrypt it.
Get Your Secret Key
Login to your iDevAffiliate admin center and go to Tools > API > REST API. Copy Secret Key.