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Understanding Digital Signatures: The Cryptography of Our Modern Way of Signing

How do digital signatures work 

Digital signatures are compared to the primal public-key of authenticating messages. Handwritten signatures have been popular and around for a long time as binding signatories to a message.

But how do digital signatures work?

A digital signature bears the similarity since it binds an entity or person to digital data so the recipient or a third party can review the authenticity of the binding.

A digital signature can, therefore, be defined as a cryptographic value that is derived from the data and allocated a secret key that is only known to the signer.

The applications in the real world require the recipient of the message to verify that the message was from the sender and that they can confirm the source of the message.

This is important for businesses since it reduces the likelihood of disagreement between sent and received digital data.

Model of Digital Signature

The digital signature system draws its structure from public-key cryptography.

Here’s how it works

Each party implementing this system owns a public-private key pair

The pair of keys used for encrypting and decrypting are different from the key pairs used for signing and verifying. Private keys are known as signature keys and public keys as verification keys.

As the signer, you input data to the hash function, which in turn generates a hash of data.

You then feed the hash value and the signature key to a signature algorithm which produces a digital signature from the provided hash data. The signature is added to the data, and they are both sent to the verifier.

The verifier then inputs the verification key and the digital signature to a verification algorithm that produces value as output.

The verifier then runs the same hash function on the data received to generate a hash value.

To verify identity, the derived hash value is compared to the output of the verification algorithm. The digital signature is deemed valid based on the comparison.

The signer cannot deny signing the data in the future since the digital signature is based on a private key for encryption that is only known to the signer.

Note that instead of signing data using a signing algorithm, hashed data is created. Due to the unique nature of the hash of data, it is used to sign in place of data.

Direct use of the hash of data for signing instead of data is efficient for the digital system.

Assuming that we are using RSA as the signing algorithm, RSA uses modular exponentiation to encrypt and sign.

Therefore signing a large amount of data can be expensive in the context of computational power and time. The hash of data is relatively smaller thus efficient to sign a hash than to sign the entire data

Importance of Digital Signature 

Digital signatures use public-key cryptography because they are essential in information security.

In addition to preventing the rejection of a message by a sender, a digital signature also ensures the integrity of data and authentication of messages.

Let's take a look at how digital signatures achieve this:

Data Integrity

In a scenario where an attacker can access data and modify it, the verification of the digital signature fails on the recipient side.

The output provided by the verification algorithm fails to match with the hash of the modified data. Therefore he/she can deny the message since the integrity of the data has been compromised.

Message authentication

If the verifier confirms the authenticity of the digital signature using the sender's public key, he can be sure that the signature belongs to the sender who has the secret private key.


Since only the signer knows the signature key, he can create a unique signature from the provided data. Hence, the recipient can use the data plus the digital signature as evidence if any disagreements arise in the future.

Embedding the public key encryption to digital signatures, a cryptosystem can be created to provide four critical elements of security: 

  • Privacy
  • Authentication
  • Non-repudiation
  • Integrity


Digital signatures for encryption

It is crucial for digital communications to exchange encrypted messages as opposed to plain texts for confidentiality purposes.

In the public key encryption system, the public key(encryption) of the sender is available in the public domain which makes it easier for anyone to spoof the identity and send an encrypted message to the receiver.

It is therefore essential for users of the public-key encryption system to implement digital signatures to ensure the authentication of messages and non-repudiation.

This is achievable by integrating the digital signature with the public key encryption system.

There are two ways to do this: 

  • Signing then encrypting
  • Encrypting then signing

The cryptosystem based on “signing then encrypting” is prone to spoofing attacks by the receiver whereby by spoofing the identity of the sender he/she can send that data to third parties.Hence, it is not a good idea to implement this method.

The “encryption then signing” method involves the recipient receiving the encrypted data with a digital signature on it; he/she first verifies the signature using a public key from the sender. After validating the signature, they can then retrieve the data by decryption using the private key.

Key management

The security of a cryptosystem highly depends on the protection of key management. Without the necessary security procedures involved in handling cryptographic keys, we can't enjoy the advantages of a strong cryptographic system.

Cryptographic systems are difficult to penetrate because of design. However, they are prone to attacks due to poor key management.

Cryptographic keys are unique pieces of data, and the process of key management entails the secure administration and management of cryptographic keys. In public key cryptography, there are two critical factors of key management 

How secret are the public keys?

The private and public keys should remain a secret to all parties except the authorized parties and the signature owner.

The validity of public keys. 

In PKC, public keys exist in the public domain and viewed publicly. Therefore, one cannot be sure of the authenticity of a public key, the valid sender, or its use. Hence, the management of public keys should be a priority to ensure their authenticity.

Final Note

Due to the use of Digital signatures are the next big solution for secure communication and authentication of transactions. It is therefore vital for you as a business owner to integrate this system to ensure the security of your communications and transactions.


Contributor: admin
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