What are the differences between RSA, DSA, and ECC encryption algorithms?

RSA, DSA, and ECC encryption algorithms are the primary algorithms used for generating keys in public key infrastructure.

Public key infrastructure (PKI) is used to manage identity and security in internet communications and computer networking. The core technology enabling PKI is public key cryptography, an encryption mechanism that relies upon the use of two related keys, a public key, and a private key.

This public and private key pair is together encrypting and decrypting messages. Pairing two cryptographic keys in this manner is also known as asymmetric encryption, which is different from symmetric encryption, in which a single key is used for both encryption and decryption.

The advantage of asymmetric encryption is that the public key can be published for the world to see, while the private key is kept secure on the user's device, making it much more secure than symmetric encryption.

How public key cryptography relies on encryption

Public key cryptography relies on mathematical algorithms to generate the keys. The public key consists of a string of random numbers that can be used to encrypt a message. Only the intended recipient can decipher and read this encrypted message and it can only be deciphered and read by using the associated private key, which is secret, and known only to the recipient.

Public keys are created using a complex cryptographic algorithm to pair them with their associated private key so that they cannot be exploited through a brute force attack.

The key size or bit length of public keys determines the strength of protection. For example, 2048-bit RSA keys are often employed in SSL certs, digital signatures, and other digital certificates. This key length offers sufficient cryptographic security to keep hackers from cracking the algorithm. Standards organizations like the CA/Browser Forum define baseline requirements for supported key sizes.

PKI enables the digital certificates that we encounter daily, unobtrusively and ubiquitously, when using websites, mobile apps, online documents, and connected devices. One of the most common use cases of PKI is X.509-based Transport Layer Security (TLS)/Secure Socket Layer (SSL). This is the basis of the HTTPS protocol, which enables secure web browsing. But digital certificates are also applied to a wide range of use cases including application code signing, digital signatures, and other aspects of digital identity and security.

What are the RSA, DSA, and ECC algorithms?

There are three primary algorithms used for PKI key generation:

• Rivest–Shamir–Adleman (RSA)
• Digital signature algorithm (DSA)
• Elliptic curve cryptography (ECC)

RSA vs ECC vs DSA algorithms

The RSA algorithm was developed in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman. It relies on the fact that factorization of large prime numbers requires significant computing power, and was the first algorithm to take advantage of the public key/private key paradigm. There are varying key lengths associated with RSA, with 2048-bit RSA key lengths being the standard for most websites today.

ECC encryption is based on mathematical algorithms governing the algebraic structure of elliptic curves over finite fields. It provides equivalent levels of cryptographic strength as RSA and DSA, with shorter key lengths. ECC was the most recently-developed encryption method of the three, with Elliptic Curve Digital Signature Algorithm (ECDSA) becoming accredited in 1999, and Key Agreement and Key Transport Using Elliptic Curve Cryptography following in 2001. Like DSA, ECC is FIPS-certified, and is also endorsed by the National Security Agency (NSA).

DSA encryption uses a different algorithm than RSA to create public key/private keys, based on modular exponentiation and the discrete logarithm problem. It provides the same levels of security as RSA for equivalent-sized keys. DSA was proposed by the National Institute of Standards and Technology (NIST) in 1991 and was adopted by the Federal Information Processing Standard (FIPS) in 1993.

Note that it's possible to support multiple encryption algorithms at the same time. For example, Apache servers can support both RSA- and DSA-generated keys on the same server. Taking such a "belts and suspenders" approach enhances your enterprise security.

How do RSA and DSA compare?

While RSA and DSA use different types of mathematical algorithms to generate the key pairs, for purposes of cryptographic strength, both are considered to be equivalent. Instead, the main differences between RSA and DSA come down to performance and speed.

Performance and speed

RSA is faster than DSA when it comes to encrypting and signing, but is slower than DSA for decrypting and verifying. However, since authentication requires both, for many real-world applications the performance difference is largely negligible.

RSA is also slower than DSA when it comes to key generation, but since keys are generated once and used for months or years, this is often not an important consideration.

SSH protocol support

Another difference can be found in their Secure Shell (SSH) protocol support. RSA is compatible with both the original SSH, as well as the newer, second edition SSH2, while DSA only works with SSH2. As SSH is not considered to be as safe as SSH2, that may be a consideration for using DSA.

Federal endorsement

Another difference between DSA and RSA is that DSA is endorsed by the U.S. Federal Government. For businesses providing services to federal agencies, the ability to keep up with government standards may be an argument for using DSA.

The bottom line is that for most use cases, industries, and regulatory environments, RSA and DSA are very similar, offering equivalent cryptographic strength, and there is relatively little difference between the two. The two algorithms are also equally compatible with leading internet protocols including Nettle, OpenSSL, wolfCrypt, Crypto++, and cryptlib.

How does ECC compare to RSA and DSA?

The biggest difference between ECC and RSA/DSA is the greater cryptographic strength that ECC offers for equivalent key size. An ECC key is more secure than an RSA or DSA key of the same size.

Key size comparison:

Symmetric Key Size (bits)	RSA Size (bits)	Elliptic Curve Key Size (bits)
80	1024	160
112	2048	224
128	3072	256
192	7680	384
256	15360	521

Recommended Key Sizes According to NIST

ECC is more efficient

As the figure shows, with ECC you get equivalent cryptographic strength with significantly smaller key sizes - about an order of magnitude smaller. For example, to achieve the equivalent cryptographic strength of encrypting using a 112 bit symmetric key would require an RSA 2048 bit key, but only an ECC 224 bit key.

The shorter key lengths mean devices require less processing power to encrypt and decrypt data, making ECC a good fit for mobile devices, Internet of Things, and other use cases with more limited computing power.

Security and speed

There are also some advantages to ECC compared to RSA or DSA in more traditional use cases like web servers, as smaller key sizes enable stronger security with faster SSL handshakes, which translates to faster web page load times.

It’s worth noting that ECDSA, the original version of ECC, is a variant of DSA. ECDSA offers equivalent levels of cryptographic strength per number of bits as ECC.

Why is elliptic curve cryptography not widely used?

While RSA is the most widely used algorithm, ECC has been gaining popularity over the years. One of the simpler reasons for RSA’s dominance is that it has been around longer. That being said, there are some cons to ECC that could further explain why people avoid it:

• Complexity: Learning and adopting ECC takes more time and is a more complex process than RSA. This can increase the risk of errors, which will have a negative impact on cybersecurity.

• Vulnerabilities: ECC can be vulnerable to side-channel attacks (SCA), which can lead to brute force attacks. They can also be vulnerable to twist security attacks, though there are countermeasures to help prevent these attacks.

Quantum computing and the future of encryption algorithms

With quantum computing on the horizon, we can expect a large shift in cryptographic security measures. Classical cryptographic algorithms like RSA and ECC will easily be broken by quantum computing, making it crucial for organizations to adapt to new encryption methods. Luckily, new algorithms have already been developed.

NIST evaluated current post-quantum cryptography (PQC) algorithms and determined four winners: ML-KEM (formerly CRYSTALS-Kyber), and CRYSTALS-Dilithium, FALCON, and SPHINCS+. Keeping up-to-date on advancements in these algorithms, and new standardization practices, will be essential for organizations moving forward.

Now that you have become more familiar with RSA, DSA, and ECC encryption algorithms; contact us today to learn more about how our products can protect your website from security threats. We also recommend exploring Sectigo’s PQC solutions.