Passkeys leverage public-key cryptography to enhance login security. Instead of passwords, they utilize a private key stored on the user's device and a corresponding public key registered with the online service. During login, the device uses its private key to sign a challenge issued by the service, proving possession of the correct key without ever transmitting it. This process, based on established cryptographic principles and protocols like WebAuthn, eliminates the vulnerability of transmitting passwords and mitigates phishing attacks, as the private key never leaves the user's device and is tied to a specific website. This model ensures only the legitimate device can authenticate with the service.
The Trail of Bits blog post, "The Cryptography Behind Passkeys," delves into the intricate cryptographic mechanisms that underpin the functionality and security of passkeys, a novel authentication technology poised to supplant passwords. The post meticulously dissects the two primary cryptographic operations at the heart of passkeys: authenticator registration and authentication.
During authenticator registration, a new cryptographic key pair is generated. This key pair consists of a private key, securely stored within the authenticator (e.g., a hardware security key or a platform authenticator like those integrated into operating systems), and a corresponding public key. Crucially, the private key never leaves the authenticator, significantly enhancing security. This public key is then registered with the online service the user is signing up for. The post emphasizes the diverse range of algorithms supported for key generation, including the widely adopted Elliptic Curve Cryptography (ECC) with curves like P-256, and highlights the importance of algorithm agility for future-proofing passkeys against potential vulnerabilities discovered in specific algorithms.
The authentication process, triggered when a user attempts to log in, involves a challenge-response protocol. The online service sends a challenge, essentially a random piece of data, to the authenticator. The authenticator then uses its stored private key to cryptographically sign this challenge. This digital signature, along with user presence confirmation (often a biometric check or a PIN), is transmitted back to the service. The service then verifies the signature using the previously registered public key, confirming the user's identity. This process assures the service that the response originated from the authenticator holding the corresponding private key without ever transmitting the private key itself.
The blog post also explicates the role of attestation in bolstering passkey security. Attestation provides cryptographic proof of the authenticator's provenance and characteristics, allowing the online service to verify that the authenticator is genuine and adheres to specific security standards. This mitigates the risk of malicious or compromised authenticators being used. Different levels of attestation, such as basic attestation and self attestation, offer varying degrees of assurance and are described in detail.
Furthermore, the post touches upon the concept of hybrid authenticators, which combine aspects of platform and roaming authenticators, leveraging a cloud synchronization mechanism to enable cross-device functionality. This involves securely syncing the private key across multiple devices belonging to the same user, introducing complexities in key management and requiring robust cryptographic protections to safeguard the synchronized keys.
Finally, the post underscores the potential benefits of passkeys in combating phishing attacks, a significant security threat in the current password-based authentication landscape. By eliminating the need for users to enter passwords, passkeys effectively remove the vulnerability associated with users inadvertently disclosing their credentials to fraudulent websites. The cryptographic underpinnings of passkeys ensure that authentication is tied to a specific legitimate website, thwarting attempts by malicious actors to impersonate legitimate services and steal user credentials.
Summary of Comments ( 78 )
https://news.ycombinator.com/item?id=43983159
Hacker News users discussed the practicality and security implications of passkeys. Some expressed concern about vendor lock-in and the reliance on single providers like Apple, Google, and Microsoft. Others questioned the robustness of the recovery mechanisms and the potential for abuse or vulnerabilities in the biometric authentication process. The convenience and improved security compared to passwords were generally acknowledged, but skepticism remained about the long-term viability and potential for unforeseen issues with widespread adoption. A few commenters delved into the technical details, discussing the cryptographic primitives used and the specific aspects of the FIDO2 standard, while others focused on the user experience and potential challenges for less tech-savvy users.
The Hacker News post titled "The Cryptography Behind Passkeys" (https://news.ycombinator.com/item?id=43983159) has generated a moderate number of comments discussing various aspects of passkeys and their implementation.
Several commenters delve into the technical details of the cryptographic processes involved. One commenter clarifies the distinction between the private key never leaving the device and the public key being shared, emphasizing the security implications of this asymmetric cryptography. Another commenter questions the article's choice of elliptic curves, advocating for the use of Curve25519 due to its performance advantages and perceived security benefits. A related discussion thread emerges regarding the security considerations of using specific elliptic curves and the potential vulnerabilities they might present.
Practical implications and user experiences are also discussed. One commenter raises the issue of account recovery and how passkeys handle situations where a user loses access to their device. Another commenter expresses concern about the user experience of passkeys, especially during the initial setup and login processes. The potential for increased security and the elimination of passwords are acknowledged as benefits, but the commenter argues that a smoother user experience is crucial for widespread adoption. The topic of platform lock-in is also brought up, with commenters expressing concern about the potential for dependence on specific platforms and the implications for user freedom.
A few commenters offer insights into the implementation and standardization efforts around passkeys. One commenter points to the WebAuthn standard and FIDO2 as key components of the passkey ecosystem, highlighting the importance of open standards in ensuring interoperability. Another commenter mentions the challenges of cross-device compatibility and the need for seamless integration across different operating systems and browsers. A brief discussion arises about the role of biometrics in passkey authentication and the potential security and privacy trade-offs.
Overall, the comments section provides a valuable discussion of the technical, practical, and user-centric aspects of passkeys. The commenters explore the nuances of the cryptographic mechanisms, the potential benefits and drawbacks of passkey adoption, and the challenges of implementing a secure and user-friendly system. While some comments offer praise for the advancements offered by passkeys, others express reservations and concerns about specific implementation details and the potential for unforeseen issues.