--- title: "Understanding DKIM’s cryptographic algorithms: RS256 vs. RS512 and emerging trends | AutoSPF" description: "When it comes to maintaining the integrity of the contents of an email and verifying that they genuinely come from a trusted sender." image: "https://autospf.com/og/blog/understanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends.png" canonical: "https://autospf.com/blog/understanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends/" --- Quick Answer When it comes to maintaining the integrity of the contents of an email and verifying that they genuinely come from a trusted sender, DKIM is the authentication protocol that most security teams trust. This email authentication standard operates on cryptographic algorithms to generate a digital signature on each email. ## Try Our Free DKIM Lookup Auto-discover DKIM selectors for any domain. [ Discover DKIM Selectors → ](/tools/dkim-lookup/) Share [ ](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fautospf.com%2Fblog%2Funderstanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends%2F "Share on LinkedIn") [ ](https://twitter.com/intent/tweet?text=Understanding%20DKIM%E2%80%99s%20cryptographic%20algorithms%3A%20RS256%20vs.%20RS512%20and%20emerging%20trends&url=https%3A%2F%2Fautospf.com%2Fblog%2Funderstanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends%2F "Share on X/Twitter") [ ](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fautospf.com%2Fblog%2Funderstanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends%2F "Share on Facebook") [ ](https://reddit.com/submit?url=https%3A%2F%2Fautospf.com%2Fblog%2Funderstanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends%2F&title=Understanding%20DKIM%E2%80%99s%20cryptographic%20algorithms%3A%20RS256%20vs.%20RS512%20and%20emerging%20trends "Share on Reddit") [ ](mailto:?subject=Understanding%20DKIM%E2%80%99s%20cryptographic%20algorithms%3A%20RS256%20vs.%20RS512%20and%20emerging%20trends&body=Check out this article: https%3A%2F%2Fautospf.com%2Fblog%2Funderstanding-dkims-cryptographic-algorithms-rs256-vs-rs512-and-emerging-trends%2F "Share via Email") ![cryptographic algorithms](https://media.mailhop.org/autospf/images/2024/10/spf-record-tester-1500.jpg) When it comes to maintaining the integrity of the contents of an email and verifying that they genuinely come from a trusted sender, DKIM is the authentication protocol that most security teams trust. This [email authentication](/spf-too-many-dns-lookups/spf-lookup/) standard operates on [cryptographic algorithms](https://www.geeksforgeeks.org/basics-of-cryptographic-algorithms/) to generate a [digital signature](https://www.techopedia.com/definition/5426/digital-signature) on each email. _DKIM ([RFC 6376](https://datatracker.ietf.org/doc/html/rfc6376)) signs email messages cryptographically, and unlike SPF, the signature survives email forwarding - which is why DMARC alignment via DKIM is more reliable than SPF alignment for forwarded mail and mailing lists._ Learn more in our [comprehensive DKIM guide](/blog/what-is-dkim-email-authentication-guide/). _In this way, the recipient can authenticate the sender and ensure that the message content has not been tampered with during transit_. Once the recipient has this confirmation that the incoming email is indeed from a reliable source, they can rest assured that it does not bring along any phishing or [spoofing threats](https://www.welivesecurity.com/2020/11/26/fbi-warning-domains-spoofing-websites/). In this article, we’ll look at what goes behind this authentication protocol, particularly focusing on DKIM’s two cryptographic algorithms. To start off, explore the two major algorithms used by DKIM - RS256 and RS512, which combine [RSA encryption](https://www.bleepingcomputer.com/news/security/new-attack-recovers-rsa-encryption-keys-from-em-waves-within-seconds/) with SHA-256 and SHA-512 hashing functions, respectively. _The job of both these algorithms is to protect the integrity and authenticity of email content, but they differ in key areas, such as security strength, processing requirements, and compatibility. Let’s delve deeper into this_. ## How does DKIM use cryptographic algorithms for email security? When an email goes out from the sender’s end, DKIM creates a digital signature with the help of cryptographic algorithms, which in turn, generate a unique hash of certain parts of the email message, such as the ‘From’ and ‘Subject’ lines, and then encryptes it with its [private key](https://www.techtarget.com/searchsecurity/definition/private-key). The signature is then attached to the [header of the message](https://www.8p-design.com/en/blog/how-read-and-understand-email-message-header). When the email reaches the receiver, its server decrypts the signature in the email to retrieve the original hash by using the [public key](https://www.investopedia.com/terms/p/public-key.asp) of the sender from the DNS of the sender. _It then compares this hash with one it generates itself from the email received. If the two hashes match, the email is considered genuine and not spoofed_. ## How are RS256 and RS512 different than each other? RS256 and RS512 are two cryptographic algorithms used in DomainKeys Identified Mail (DKIM) for authenticating and ensuring the [integrity of emails](https://www.libraesva.com/blog-can-you-prove-the-integrity-of-your-emails-in-court-resolving-disputes-and-legal-proceedings/). _The differences between them mainly lie in the hashing function used, which affects their strength in security, processing performance, and compatibility_. Let’s take a closer look at each of them: ### RS256 (RSA with SHA-256) #### Security RS256 is a standard DKIM algorithm, most commonly used to secure [email communication](https://writingcenter.unc.edu/tips-and-tools/effective-e-mail-communication/). It uses SHA-256 to generate a 256-bit hash that protects against hash collisions. This level of strength ensures that a hash value cannot be forged to produce a similar counterfeit message, thereby safeguarding its integrity. ![Email deliverability](https://media.mailhop.org/autospf/images/2024/10/spf-validator-2475.jpg) #### Performance Performance-wise, the RS256 is quite efficient even with RSA key sizes over 2048 bits. It works well because of its [SHA-256](https://www.ssldragon.com/blog/sha-256-algorithm/) hashing function. This function has a relatively short hash at 256 bits, which enables very fast processing and verification of signatures. Since the hash length is relatively shorter, RS256 consumes less computing power than larger hash algorithms, making it suitable for high-volume environments where email throughput is critical. #### Compatibility With RS256, you don’t have to worry about compatibility issues, as it supports virtually all modern and legacy email systems. This means that it works effectively across a variety of different infrastructure configurations, making it a widely adopted algorithm. ### RS512 (RSA with SHA-512) #### Security RS512 uses SHA-512, which creates a 512-bit hash. This offers much better in terms of security when compared to SHA-256\. This makes the former highly resistant to [brute force attacks](https://www.bbc.com/news/uk-scotland-scotland-politics-40941722) as well as [collision attacks](https://www.bleepingcomputer.com/news/security/google-announces-first-ever-sha1-collision-attack/). It is very useful for organizations that have very strict security requirements or deal with [sensitive data](https://www.imperva.com/learn/data-security/sensitive-data/). #### Performance Although it provides more security, the computational load is higher with RS512 than with RS256 because the hash size is bigger. _It may lead to a slight delay in processing, and this might cause a difference in high-volume email operations_. However, if your organization prioritizes security over speed, [RS512](https://stackoverflow.com/questions/54378165/how-do-i-implement-rs512-or-higher-security-algorithm-in-php-rest-website) is the apt choice for you. #### Compatibility Given the higher computational load of this algorithm, RS512 may not be well supported by older [email servers](https://www.one.com/en/email/what-is-an-email-server) or systems that haven’t optimized for SHA-512\. _If you want the enhanced level of security that RS512 provides, it is important that you upgrade your infrastructure that is compatible with it_. ## What are the emerging trends in DKIM cryptographic algorithms? [Cyberattacks](https://cybersecuritynews.com/nist-finalised-3-encryption-tools-for-quantum-cyberattacks/) are getting more frequent and severe, which means that traditional techniques are no longer capable of keeping up with the growing threats. New trends in DKIM cryptographic algorithms that are pushing [email security](/) to new levels of resilience and efficiency. ### Elliptic Curve Cryptography (ECC) These days, [ECC](https://www.digicert.com/faq/cryptography/what-is-elliptic-curve-cryptography) is being preferred over [RSA-based cryptography](https://blog.cloudflare.com/how-the-nsa-may-have-put-a-backdoor-in-rsas-cryptography-a-technical-primer/) as it offers sound security with much smaller key sizes. _For instance, if you use a 256-bit elliptic curve, it would provide comparable security to a 3072-bit RSA key but take significantly less time for verification_. ![Elliptic Curve Cryptography (ECC) ](https://media.mailhop.org/autospf/images/2024/10/spf-record-generator-3.jpg) ### Automated key rotation One of the best things you can do to protect your [email infrastructure](https://www.voilanorbert.com/blog/email-infrastructure/) with DKIM is to rotate keys regularly. With DKIM’s automated key rotation, you don’t have to worry about doing it manually. This rotation feature regularly replaces the public and private keys without human intervention to further improve security by limiting each key’s lifespan and making it harder for attackers to crack the keys. ### Quantum-resistant algorithms You’d be surprised to know that [quantum computing](https://en.wikipedia.org/wiki/Quantum%5Fcomputing) has the potential to break most traditional cryptographic algorithms, such as RSA and ECC. Even though it is an emerging technology, quantum computers theoretically break these systems much more easily than their classical counterparts. This is why we need something that is far more robust and resistant to quantum algorithms. Research into quantum-resistant algorithms is underway to future-proof DKIM from the threats of quantum computing and ensure continued email security in a quantum-enabled future. ## To sum up As you know, [DKIM](/10-reasons-for-regular-spf-record-checks-in-cybersecurity/dkim-record-check/) is one of the most crucial authentication protocols that ensures the integrity of emails. _By using standards like RS256 and RS512, DKIM offers you the flexibility to choose the level of security you want for your email communications_. But given the ever-evolving threat landscape, it is crucial that you keep upgrading your security strategies. To get started with DKIM implementation, [book a demo](/book-a-demo/) with us today! ## Topics [ DKIM ](/tags/dkim/)[ email security ](/tags/email-security/) ![Brad Slavin](https://media.mailhop.org/autospf/images/authors/brad-slavin.jpg) [ Brad Slavin ](/authors/brad-slavin/) General Manager Founder and General Manager of DuoCircle. Product strategy and commercial lead for AutoSPF's 2,000+ customer base. [LinkedIn Profile →](https://www.linkedin.com/in/bradslavin) ## Ready to get started? Try AutoSPF free — no credit card required. [ Book a Demo ](/book-a-demo/) ## Related Articles [ Advanced 8m What is the ‘554 5.7.5’ permanent error in DMARC and how to fix it? Jul 9, 2024 ](/blog/554-5-7-5-permanent-error-in-dmarc-and-how-to-fix-it/)[ Advanced 6m 8 cybersecurity trends that will redefine the digital landscape in 2024 Sep 20, 2024 ](/blog/8-cybersecurity-trends-that-will-redefine-the-digital-landscape-in-2024/)[ Advanced 17m AI-Powered Phishing in 2026: How Generative AI Changed the Attacker Economics of Email Why Email Authentication Is the Last Reliable Defense Signal in the Age of AI May 4, 2026 ](/blog/ai-powered-phishing-2026-email-authentication-last-ai-defense-signal/)[ Advanced 10m AutoSPF’s Guide to Configuring SPF & DKIM for Avanan: A Detailed Walk-through Nov 26, 2025 ](/blog/autospf-guide-configuring-spf-dkim-for-avanan-detailed-setup-walkthrough/) ```json {"@context":"https://schema.org","@type":"Organization","@id":"https://www.wikidata.org/wiki/Q138897474","name":"AutoSPF","url":"https://autospf.com","logo":{"@type":"ImageObject","url":"https://autospf.com/images/autospf-logo.png"},"description":"Automatic SPF flattening and email authentication management. 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