How Secure Is 256-bit Encryption?

Most people constantly use the term “256-bit encryption” and, to be honest, have absolutely no idea what it means and how reliable it is. Once you get beyond the surface level, “it encrypts data and makes it unreadable,” encryption becomes an incredibly difficult task. 

That’s why it’s understandable that there may be some confusion when it comes to the strengths of encryption — what they mean, what is “good”, etc. There is no shortage of questions about encryption, especially about 256-bit encryption.

The main one is: how secure is 256-bit encryption?

So, today we will talk about this. We will tell you what even a little bit of security is, we will look at the most common form of 256-bit encryption.

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A reminder about encryption in general​

When you encrypt something, you take unencrypted data, called plaintext, and perform an algorithmic function with it to create a fragment of encrypted ciphertext. The algorithm you use is called a key. Except for public keys in asymmetric encryption, the value of the encryption key must be kept secret. The private key associated with this piece of encrypted text is the only practical means of decrypting it.

256-bit encryption security

All of this sounds incredibly abstract, so let’s look at an example. Let’s go with Jack and Diane, and let’s say Jack wants to send Diane a message that says: “Oh yes, life goes on.”

Jack will take his message and is going to use an algorithm or cipher-the encryption key-to encrypt the message into ciphertext. Now he will give it to Diana along with a key that can be used to decrypt the message so that it can be read again.

Until no one else gets the key, the encrypted text is worthless because it cannot be read.

How does modern encryption work?​

A key or a specific algorithm is used to encrypt data, and only the other party who knows the corresponding private key can decrypt it.

In this example, rather than in a written message that darkly asserts that life continues even after joy is lost, Jack and Diane are “doing everything they can” on computers. Now, the encryption that needs to happen is digital.

Jack’s computer will use its key, which is actually an extremely complex algorithm derived from data shared by Jack and Diane’s devices, to encrypt plaintext. Diane uses her corresponding symmetric key to decrypt and reads the data.

Asymmetric encryption and symmetric encryption​

Symmetric encryption is sometimes called private key encryption because both parties must share a symmetric key that can be used for both encryption and decryption of data.

On the other hand, asymmetric encryption is sometimes called public key encryption. It’s better to think of asymmetric encryption as one-way encryption.

Unlike the fact that both parties share a private key, there is a pair of keys. One side has a public key that can be encrypted, the other has a private key that can be decrypted.

Asymmetric encryption is mainly used as a mechanism for exchanging symmetric private keys. There is a reason for this: asymmetric encryption has historically been a more expensive feature due to the size of its keys. So public key cryptography is used more like an external wall to help protect the parties as they facilitate the connection, while symmetric encryption is used in the actual connection itself.

2048-bit keys vs. 256-bit keys​

In SSL/TLS, asymmetric encryption performs one extremely important function. This allows the client to encrypt data that will be used by both parties to obtain symmetric session keys that they will use for communication.

Is secure 256-bit encryption

You will never be able to use asymmetric encryption for functional communication. Although a public key can be used to verify a digital signature, it cannot directly decrypt anything that is encrypted with a private key, which is why we call asymmetric encryption “one-way.”

But the bigger problem is that the size of the key makes the actual encryption and decryption functions expensive in terms of the CPU resources they consume. That’s why many large organizations and enterprises have unloaded handshakes when deploying SSL/TLS on a large scale: to free up resources on their application servers.

Instead, we use symmetric encryption for the actual interaction that occurs during the encrypted connection. Symmetric keys are smaller and cheaper to compute.

So, when you see someone refer to a 2048-bit private key, they most likely mean the RSA private key. This is an asymmetric key. It should be sufficiently resistant to attacks since it performs such an important function. In addition, key exchange is the best attack vector for compromising the connection. 

It is much easier to steal the data used to create a symmetric session key and calculate it yourself than to crack the key by brute force after it is already in use.

The question arises: “How reliable is 256-bit encryption?” If it is less reliable than a 2048-bit key, is it enough?

How secure is 256-bit encryption?​

It depends on the algorithm you are using and from asymmetric to symmetric encryption. As we have already said, this is not 1:1 comparison. The security level of asymmetric encryption is not as scientific as it might seem. 

Asymmetric encryption is based on mathematical problems that are easy to solve in one direction (encryption), but extremely difficult to reverse (decryption). Because of this, public key attacks, and asymmetric cryptosystems tend to be much faster than brute force key space search, which interferes with private key and symmetric encryption schemes. 

So, when you talk about the security level of public key cryptography, this is not an established figure, but a calculation of the computational strength of the implementation against the best, most currently known attack.

The level of symmetric encryption is a little easier to calculate because of the nature of the attacks they need to defend against.

Let’s take a look at AES or Advanced Encryption Standard, which is commonly used as bulk encryption with SSL/TLS. Mass ciphers are symmetric cryptosystems that actually ensure the security of communication that occurs during an encrypted HTTPS connection.

Historically, there are two varieties: block ciphers and stream ciphers.

Block ciphers break everything they encrypt into key-sized blocks and encrypt them. Decryption involves connecting blocks together. And if the message is too short or too long, which happens in most cases, it needs to be split and/or supplemented with one-time data to make them of suitable length.


Digital cryptography has improved significantly over the years. However, today AES (Advanced Encryption Standard) is the best choice for reliable and secure communication on the internet. Even the most cunning hacker will take millions of years to decipher the true content of messages encrypted, for example, using AES-256. 

Thus, security and confidentiality are significantly increased, so not only modern enterprises but also government organizations of the highest level trust this standard for their communications.


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