Yesterday I implemented for our FileMaker and Xojo Plugins the classes/functions to use the elliptic curve functions from OpenSSL for digital signatures.
Using those functions you can create a pair of private/public keys. Using the private key you can sign some data digitally. Later you can use our verify function to verify the signature with the public key.
Now if you want to use this to sign some data, you generate your keys. The private key is stored locally. The public key is sent to your partner, client or whoever should verify the signature.
To sign data, please make a Hash first. We use SHA-512 for most secure hashes currently. This hash is than signed and we get a signature. The public key is sent to someone once. Next you send the data with signature. Now the receiver can use the public key to verify the signature on the same data hash.
For the key generation we can choose between 79 different built-in curves with various bit numbers from 112 to 571 bit.
Read more on wikipedia. Available for FileMaker and Xojo with next plugin prerelease.