Here are links to a number of live-to-web cryptographic toy engines for you to experiment with. I have attempted to include a working engine, ALGORITHM (in Pseudocode) and a link that lets you examine the PHP code I wrote to implement each algorithm. Comments/suggestions are welcome.
Related encryption examples
Where the same "key" is used to encrypt and decrypt messages - security of the key is the make/break of these ciphers.
stolen from https://www.ssl2buy.com/wiki/symmetric-vs-asymmetric-encryption-what-are-differences
Where there are different keys for encryption/decryption ("public"/"private"). This way "anyone" can encrypt a message using the public key, but only those with the secret key can decrypt it.
stolen from https://www.ssl2buy.com/wiki/symmetric-vs-asymmetric-encryption-what-are-differences