Going with the understanding that both symmetric and asymmetric encryption do not necessarily have to be encrypted/decrypted with a computer program, one can see all forms of encryption distinctly in these categories:
Symmetric Encryption
Symmetric encryption is simply an encryption that shares a single key for the encryption and decryption process. Obviously this can generally be done electronically however this category can apply to any encryption even if it wasn’t generated with a computer program. Also, it is good to note that there are two types of Symmetric key algorithms, Stream ciphers, and Block ciphers. This can also be applied to any encryption that encrypted by yourself. A good example of this could be if one decided to substitute letters for numbers (a=1, b=2, c=3, etc) to encrypt/decrypt a set of text.
A Stream Cipher is an encryption algorithm that operates on one bit (or one byte) at a time. This allows for a faster encryption and decryption time, and ease of implementation, however the only downfall from a security perspective that it has is if the same key stream is used, information that is encrypted may be revealed. A good example of this would be the VEST cipher
A Block Cipher is a category of algorithm that encrypts and decrypts data or information in blocks or sets. The data is essentially broken down and then encrypted individually in blocks. A good example of two different block ciphers that are used often today are AES and DES.
Asymmetric Encryption
Opposite of symmetric encryption, asymmetric encryption uses a separate key for the encryption and decryption processes. This is usually referred to as public key cryptography, since there is a private key that is used for encrypting data, and a public key that is used for decrypting that data. In some cases, each user is giving key-pairs of their own public and private keys so that they are able to both send and receive messages. Some good examples of asymmetric encryption are RSA, DSA, and PGP.
Keep in mind that non-software dependent algorithms can still be implemented in software. With that said, you should have a good grasp of the basics of the forms of encryption.
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