When you’re carrying out a secure electronic transaction, there’s often a digital signature at play. A Digital Signature Algorithm (DSA) can have a key role in developing that signature to help ensure that the electronic exchange of words, funds, or other data is authentic—and that it hasn’t been forged or tampered with.
Think of it this way: during medieval times, great houses used wax seals featuring their house sigil when exchanging correspondence. You can consider your digital signature in a similar way. It’s how recipients ensure that whatever information you’re exchanging is coming from you, and that it’s safe to open.
Digital signatures use public-key encryption, otherwise known as asymmetric encryption, to create a signature of mathematically related components to verify a document’s authenticity and the identification of the sender.
A bit of background on the Digital Signature Algorithm
As a Federal Information Processing Standard (FIPS), the Digital Signature Algorithm can be used to generate a digital signature, which is then used to detect unauthorized modifications to data and to authenticate the identity of the sender.
It was first proposed by NIST in 1991, and although it is a less popular cryptographic standard in today’s digital world, it is still sometimes used in areas such as email communication, software updates, and document verification.
Digital Signature Algorithm provides a system for verifying origin authentication, ensuring data integrity, and instilling non-repudiation in the process. This means that your recipient can easily see and verify that a message came from you, ensure it hasn’t been tampered with, and that you can’t dispute that it did/did not come from you.
The role asymmetric encryption plays in the Digital Signature Algorithm
Asymmetric key encryption helps provide secure, encrypted data within public channels. It involves two participants, the sender and the recipient. Each has its own pair of public/private keys.
The sender obtains the recipient’s public key and uses it to encrypt a plaintext message, creating ciphertext. That ciphertext is then sent to the recipient, who decrypts it with their private key, and returns it to legible plaintext. It’s important to note that this is a one-way transaction because you can’t read the messages of another sender, even if you have their public key.
This relationship between public and private keys plays a major role in the Digital Signature Algorithm and the mathematical formation of digital signatures.
What mathematical concepts are used in the Digital Signature Algorithm?
The Digital Signature Algorithm, like many cryptographic standards, relies heavily on the characteristics of prime numbers. However, DSA also depends on modular arithmetic, meaning that, at a certain point, numbers wrap around. You can think of that like a clock, where the numbers reset once the hands strike 12. Digital Signature Algorithms also require exponential key generation and discrete logarithmic problems.
It’s all dependent on the difficulty of the math involved. Since it’s computationally difficult to factor random prime numbers, private keys can, indeed, remain private.
To create a truly authentic digital signature, you must choose a random value and a hash to create a two-part signature. All the mathematical relations should hold true throughout the electronic exchange. That’s how you confirm authenticity—and know that your recipient can trust a message.
But why do we need digital signatures in the first place?
Understanding digital signatures
Digital signatures are bit strings that are computed using complex math and cryptographic parameters that help recipients identify senders and ensure integrity of data included in a message.
Remember: The purpose of a digital signature is to verify that a digital message is from the purported sender.
- The private key is uniquely associated with the owner of the message. It is not shared. It is used to create a digital signature.
- The public key is associated with the private key, and is made public. It is used to verify a digital signature that was generated using the private key.
- The digital signature is a mechanism that results from the public/private key data that helps verify the origin, authenticity, and integrity of the message sent.
The Digital Signature Algorithm is the system used to generate that signature and verify it, and approved DSAs are meant to keep threat actors from generating valid signatures that could be used to send forged data.
Key generation and management in the Digital Signature Algorithm
Before you can generate a digital signature using the Digital Signature Algorithm, you must first generate a public-private key pair. There are tools for simplifying this process, including cryptographic libraries.
But this is what happens:
- A random number is generated. This becomes the private key.
- That random number undergoes a series of math operations to get another number.
- The new resulting number is the public key—the one that is shared.
As you can see, the numbers are related pieces of data. The private key is the one used to create signatures. The public key is used to verify them.
Best practices for key storage, backup and rotation
To safeguard your usage of digital signatures, you must implement reliable, secure cryptographic key management. This includes keeping private keys safe and secure from unauthorized access and verifying authenticity using public keys.
Knowing where your keys are stored, who has access to them, and how they’re used can go a long way in helping safeguard cryptographic keys against misuse and compromise. Regularly rotating your keys is also important. They should be changed frequently—or immediately in the case of leaked data or industry advisories. Finally, recovery capabilities are hugely important. If you lose a key, all the data encrypted with that key will also be lost.
Signing and verifying with the Digital Signature Algorithm
How to sign a message with Digital Signature Algorithms
To sign a message with the Digital Signature Algorithm, you’ll need your key pair and what’s known as a hash function.
A hash is a mathematical function that maps a string of arbitrary length to a fixed length string. (Think of it a bit like a barcode. It represents whatever item you’re purchasing at the store with a unique identifier, the way a hash does for a message.) Hashing algorithms vary in strength, speed, and purpose, and FIPS 180-4 can provide more information about best practices and recommended hash algorithms.
You’ll use a hash function to create a message digest—a representation of the original message contents. Once you have your message digest, you’ll use your private key to sign it. The resulting combination of the hash and your private key are your signature, a unique representation of the original message, which create authenticity and ensure integrity.
Next, we’ll take a look at the other end of the process: the verification of the message.
How to verify a message using the Digital Signature Algorithm
Once your recipient receives the message, signed with your digital signature, he or she can use the shared public key to verify that signature.
If the math checks out, your signature is valid, and your recipient knows that your message is yours and can be trusted.
The Digital Signature Algorithm’s security and cryptographic strength
The security and continued cryptographic strength of the Digital Signature Algorithm relies on correct configuration, secure key management, and appropriate use. But it’s also worth noting that while considered secure due to the difficulty of the math involved, DSA is becoming less common across contemporary digital environments due to the complexity of the generation and verification process.
Potential vulnerabilities of Digital Signature Algorithms
Overall, DSA provides integrity and non-repudiation, but it still presents potential vulnerabilities.
If you reuse randomly generated numbers, you’re reducing the effectiveness of your encryption usage, and you’re giving threat actors the ability to deduce and recreate your private key.
To mitigate this: Always use a random number generator—specifically, a cryptographically secure one.
Shorter key lengths
Earlier use of Digital Signature Algorithms used a smaller maximum key size, which isn’t considered secure in a modern environment.
To mitigate this: Keys with 2048 or 3072 bits will help ensure security.
Errors in implementation can introduce vulnerabilities.
To mitigate this: Ensure that you’re following best practices and utilizing the algorithm for appropriate use cases.
Quantum computing threats
Like other public-key encryption standards, DSA is also at risk of quantum computers, which once powerful enough, will be able to solve the otherwise complex, and secure, discrete logarithm problem used in the formation of the algorithm.
To mitigate this: Take stock of quantum vulnerabilities in your organization and begin building a post-quantum cryptography migration plan. (A trusted machine identity management provider can help ensure that you have the requisite crypto-agility to thrive in a post-quantum world.)
Long-term key usage
Using the same key pair for a long time increases your risk of compromise.
To mitigate this: Regularly change and rotate keys, and always secure your keys using an HSM—and ensure strong access controls are in place. Also avoid multi-purpose keys, and set expiration dates for keys that get used frequently. Conduct regular audits, and be sure to stay updated on industry advisories.
How to implement Digital Signature Algorithms: Common use cases
As already mentioned, the popularity of the Digital Signature Algorithm has waned in favor of other algorithms, including RSA and ECDSA. However, there are a few cases for using DSA, including:
- SSL/TLS. The Digital Signature Algorithm is an option for authenticating digital signatures in SSL/TLS, but RSA is more commonly used. ECDSA has also gained more traction due to the rise in popularity of elliptic curve cryptography, for its ease of use and the level of security provided.
- SSH (Secure Shell). In more modern applications, DSA is less common due to concerns over key sizes. However, it can be used to secure remote logins and file transfers over insecure networks.
- OpenPGP. This is a data encryption and decryption protocol that provides email and file security, and it does support DSA for digital signatures.
Overall, DSA favorability has declined in recent years as professionals look for more flexible and efficient options like RSA (due to versatility and wide acceptance) or ECDSA (for efficiency and strong security).
In the next section, we’ll dive into each of these alternatives in a bit more detail.
Alternatives to using Digital Signature Algorithms
Besides Digital Signature algorithms, many rely on RSA and ECDSA for encryption and digital signature needs.
RSA is widely used, and it’s considered a staple of asymmetric encryption. It derives its security from the difficulty of factoring large integers that are the product of two large prime numbers. RSA keys are typically 1024 or 2048 bits in length, which makes them difficult to factorize. And while the process can be slow, the security is incomparable. You can learn more about RSA in this article.
ECDSA (Elliptic Curve Digital Signature Algorithm)
The Elliptic Curve Digital Signature Algorithm is one of the more complex algorithms for public key cryptography. Elliptic curve cryptography generates smaller-than-average keys, but uses the algebraic structure of elliptic curves over finite fields—more effectively performing the same functions as DSA. The math operation is quick and easy to complete, but extremely difficult to reverse, making it nearly impossible to crack private keys.
Comparing the strengths and weaknesses of DSA, RSA, and ECDSA
While all three have their best use cases and implementation practices, it’s important to remember that DSA is only for signatures, whereas RSA provides encryption, too. DSA is less common in newer systems because you must continuously ensure randomness and appropriate key implementation. And all three are vulnerable to quantum computers.
How to choose the right algorithm for your needs
Encryption is just one part of the security equation. To determine the right needs for your encryption project, perform a risk analysis. High-risk data like customer information, requires stronger encryption than something like a social media strategy.
Second, conduct a performance analysis of your network architecture and load traffic. Asymmetric encryption can be slower due to the dual-key exchange, versus the single exchange in symmetric encryption. Think about what you’re using the algorithm for, what security levels are needed, and what systems will be interacting with one another. In many cases, RSA is widely supported and offers a safe choice for consistent interoperability.
You’ll also want to consider future needs. If you need to switch algorithms later, it’s a good idea to build an algorithm-agnostic or modular system to ensure rapid migration.
Real-world Digital Signature Algorithm examples
So how are Digital Signature Algorithms used to ensure secure communication protocols and systems?
E-mail exchanges, fund transfers, and software distribution are all ways that DSA can be used throughout day-to-day operations. Any electronic exchanges that require the assurance of integrity and origin authentication may rely on DSA.
Digital signatures are legally binding, and they can ensure non-alteration in the case of digital documents like sales contacts or loan applications.
Industries that commonly use Digital Signature Algorithms
- Finance. Loan applications, mortgage paperwork, bank transfers—they all require secure communication, and DSA can be used in these instances.
- Healthcare. Secure transfers of health records across insecure public channels requires a digital signature.
- Transportation. Logistics information or shipping manifests that get signed for digitally require the use of DSA.
- Public sector. Permits and contracts require digital signatures, and can ensure that the documents have gone through proper channels and approvals.
How critical are digital signatures?
Digital signatures are an important part of secure electronic transactions, but the Digital Signature Algorithm is waning in popularity in favor of more modern, more secure cryptographic standards.
Always consider the best use cases and security of your organization when choosing encryption standards. DSA doesn’t provide maximum interoperability and compatibility, and it raises some concerns.
Regardless of which standards you implement, be sure to carefully manage encryption keys across your enterprise. Regular rotation, secure storage, and adherence to industry recommendations can help ensure your organization stays safe from data breaches and key theft.
And with the right foundation for machine identity management, you’ll be well-equipped to prepare for any encryption migrations required in a world with quantum computers.
- When Should You Use Symmetric vs Asymmetric Encryption?
- Asymmetric Encryption: What It Is and When To Use It
- What Is Encryption Key Management?
- Hashing vs Encryption: Differences and Uses