--- title: Signal's Approach to Quantum-Resistant Cryptography description: Signal deployed SPQR (Sparse Post Quantum Ratchet), a quantum-resistant cryptographic system that works alongside its existing Double Ratchet protocol to form... canonical: https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Signal's Approach to Quantum-Resistant Cryptography | daily.dev og:description: Signal deployed SPQR (Sparse Post Quantum Ratchet), a quantum-resistant cryptographic system that works alongside its existing Double Ratchet protocol to form... og:url: https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k og:image: https://api.daily.dev/og/posts/s8nxsB26K.png og:image:alt: Signal's Approach to Quantum-Resistant Cryptography og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Signal's Approach to Quantum-Resistant Cryptography **[Collections](https://daily.dev/sources/collections)** · 2 min read · 2 upvotes · 0 comments ## Summary Signal deployed SPQR (Sparse Post Quantum Ratchet), a quantum-resistant cryptographic system that works alongside its existing Double Ratchet protocol to form a Triple Ratchet. Developed with PQShield, AIST, and NYU, the system combines classical and quantum-safe keys to protect against future quantum attacks and 'harvest now, decrypt later' threats. The implementation uses X25519 and CRYSTALS-Kyber for initial key exchanges, maintains forward secrecy and post-compromise security, and has been formally verified using ProVerif and F* tools. ## Content Signal has taken a significant step toward ensuring security in the era of quantum computing by deploying a quantum-resistant cryptographic system known as SPQR (Sparse Post Quantum Ratchet). This system operates in conjunction with Signal's existing Double Ratchet protocol, forming a Triple Ratchet. This innovative design was developed alongside PQShield, AIST, and NYU, showcasing a collaborative effort to enhance cryptographic security. The SPQR system combines keys derived from both classical and quantum-safe ratchets using a key derivation function, providing dual-layered security. This ensures that messages remain protected even if either classical or quantum-based systems are compromised, effectively safeguarding communications from potential future quantum attacks. The implementation addresses the possible threat posed by 'harvest now, decrypt later' tactics, protecting initial key exchanges with a mix of traditional X25519 and CRYSTALS-Kyber in its first phase, dubbed PQXDH. Phase two of the implementation introduces SPQR into the existing Double Ratchet protocol, which not only maintains current cryptographic security but also adds a layer of quantum resistance. This ongoing development underscores Signal's commitment to forward secrecy and post-compromise security. The integration has been presented at major cryptographic conferences and uses formal verification practices with tools like ProVerif and F* to ensure correctness, setting a new benchmark for secure messaging amid the challenging landscape of quantum computing. ## Similar posts on daily.dev - [Signal Protocol and Post-Quantum Ratchets](https://daily.dev/posts/signal-protocol-and-post-quantum-ratchets-37ajp56j2) · Hacker News · 5 upvotes · 0 comments --- Tags: [#cryptography](https://daily.dev/tags/cryptography), [#encryption](https://daily.dev/tags/encryption), [#quantum-computing](https://daily.dev/tags/quantum-computing), [#security](https://daily.dev/tags/security) [View this post on daily.dev](https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Signal's Approach to Quantum-Resistant Cryptography","url":"https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k"},"datePublished":"2025-10-29T11:50:56.436Z","dateModified":"2026-03-15T03:21:30.890Z","description":"Signal deployed SPQR (Sparse Post Quantum Ratchet), a quantum-resistant cryptographic system that works alongside its existing Double Ratchet protocol to form...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/98bd657df18f0c1783f4ade5a98eb7e3?_a=AQAEulh","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/98bd657df18f0c1783f4ade5a98eb7e3?_a=AQAEulh","isAccessibleForFree":true,"articleSection":"Collections","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Collections","logo":"https://media.daily.dev/image/upload/s--fk_6ycEi--/f_auto,q_auto/v1780996001/logos/collections?_a=BAMAMiWQ0","url":"https://daily.dev/sources/collections"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/signal-s-approach-to-quantum-resistant-cryptography-s8nxsb26k","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":2},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"cryptography,encryption,quantum-computing,security","timeRequired":"PT2M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Collections","item":"https://daily.dev/sources/collections"},{"@type":"ListItem","position":3,"name":"Signal's Approach to Quantum-Resistant Cryptography"}]} ```