Encryption is a method of turning data into an unusable form that can be made useful only by means of decryption. The purpose is to make data available solely to those who can decrypt it (i.e. make it usable). Typically, data needs to be encrypted to make sure it cannot be obtained in case of unauthorized access. It is the last line of defense after an attacker has managed to break through authorization systems and access control.
This doesn't mean all data needs to be encrypted, because often times authorization and access systems may be enough, and in addition, there is a performance penalty for encrypting and decrypting data. If and when the data gets encrypted is a matter of application planning and risk assessment, and sometimes it is also a regulatory requirement, such as with HIPAA or GDPR.
Data can be encrypted at-rest, such as on disk, or in transit, such as between two parties communicating over the Internet.
Here you will learn how to encrypt and decrypt data using a password, also known as symmetrical encryption. This password must be known to both parties exchanging information.
To properly and securely use encryption, there are a few notions that need to be explained.
A cipher is the algorithm used for encryption. For example, AES256 is a cipher. The idea of a cipher is what most people will think of when it comes to encryption.
A digest is basically a hash function that is used to scramble and lengthen the password (i.e. the encryption key) before it's used by the cipher. Why is this done? For one, it creates a well randomized, uniform-length hash of a key that works better for encryption. It's also very suitable for "salting", which is the next one to talk about.
The "salt" is a method of defeating so-called "rainbow" tables. An attacker knows that two hashed values will still look exactly the same if the originals were. However, if you add the salt value to hashing, then they won't. It's called "salt" because it's sort of mixed with the key to produce something different. Now, a rainbow table will attempt to match known hashed values with precomputed data in an effort to guess a password. Usually, salt is randomly generated for each key and stored with it. In order to match known hashes, the attacker would have to precompute rainbow tables for great many random values, which is generally not feasible.
You will often hear about "iterations" in encryption. An iteration is a single cycle in which a key and salt are mixed in such a way to make guessing the key harder. This is done many times so to make it computationally difficult for an attacker to reverse-guess the key, hence "iterations" (plural). Typically, a minimum required number of iterations is 1000, but it can be different than that. If you start with a really strong password, generally you need less.
IV (or "Initialization Vector") is typically a random value that's used for encryption of each message. Now, salt is used for producing a key based on a password. And IV is used when you already have a key and now are encrypting messages. The purpose of IV is to make the same messages appear differently when encrypted. Sometimes, IV also has a sequential component, so it's made of a random string plus a sequence that constantly increases. This makes "replay" attacks difficult, which is where attacker doesn't need to decrypt a message; but rather an encrypted message was "sniffed" (i.e. intercepted between the sender and receiver) and then replayed, hoping to repeat the action already performed. Though in reality, most high-level protocols already have a sequence in place, where each message has, as a part of it, an increasing packet number, so in most cases IV doesn't need it.
This example uses Golf framework. Install it first.
To run the examples here, create an application "enc" in a directory of its own (see mgrg for more on Golf's program manager):
mkdir enc_example cd enc_example gg -k encCopied!
To encrypt data use encrypt-data statement. The simplest form is to encrypt a null-terminated string. Create a file "encrypt.golf" and copy this:
begin-handler /encrypt public set-string str = "This contains a secret code, which is Open Sesame!" // Encrypt encrypt-data str to enc_str password "my_password" p-out enc_str @ // Decrypt decrypt-data enc_str password "my_password" to dec_str p-out dec_str @ end-handlerCopied!
You can see the basic usage of encrypt-data and decrypt-data. You supply data (original or encrypted), the password, and off you go. The data is encrypted and then decrypted, yielding the original.
