Editing Internet Key Exchange (section)

==Vulnerabilities==
Leaked [[NSA]] presentations released in 2014 by {{lang|de|[[Der Spiegel]]}} indicate that IKE is being exploited in an unknown manner to decrypt IPsec traffic, as is ISAKMP.<ref>{{citation|publisher=NSA via 'Der Spiegel'|url=http://www.spiegel.de/media/media-35529.pdf|page=5|title=Fielded Capability: End-to-end VPN SPIN9 Design Review}}</ref> The researchers who discovered the [[Logjam (computer security)|Logjam attack]] state that breaking a 1024-bit Diffie–Hellman group would break 66% of VPN servers, 18% of the top million HTTPS domains, and 26% of SSH servers, which the researchers claim is consistent with the leaks.<ref>{{Cite conference| url=https://weakdh.org/imperfect-forward-secrecy-ccs15.pdf | first1=David | last1=Adrian | first2=Karthikeyan | last2=Bhargavan | first3=Zakir | last3= Durumeric | first4=Pierrick | last4=Gaudry | first5=Matthew | last5=Green | first6=J. Alex | last6=Halderman | first7=Nadia | last7=Heninger |author7-link= Nadia Heninger | first8=Drew | last8=Springall | first9=Emmanuel | last9=Thomé | first10=Luke | last10=Valenta | first11=Benjamin | last11=VanderSloot | first12=Eric | last12=Wustrow | first13=Santiago | last13=Zanella-Béguelin | first14=Paul | last14=Zimmermann | title=Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice | conference=22nd ACM Conference on Computer and Communications Security (CCS ’15) | location=[[Denver]] | date=October 2015 | access-date=15 June 2016}}</ref> This claim was refuted in 2015 by both Eyal Ronen and [[Adi Shamir]] in their paper "Critical Review of Imperfect Forward Secrecy"<ref>{{ Cite web | url=http://www.wisdom.weizmann.ac.il/~eyalro/RonenShamirDhReview.pdf | first1=Eyal | last1=Ronen | first2=Adi | last2=Shamir | title=Critical Review of Imperfect Forward Secrecy | date=October 2015}}</ref> and by Paul Wouters of Libreswan in a 2015 article "66% of VPN's{{sic}} are not in fact broken".<ref>{{ Cite web | url=https://nohats.ca/wordpress/blog/2015/10/17/66-of-vpns-are-not-in-fact-broken/ | first1=Paul | last1=Wouters | title=66% of VPN's are not in fact broken | date=October 2015}}</ref>

IPsec VPN configurations which allow for negotiation of multiple configurations are subject to [[ Man-in-the-middle_attack| MITM]]-based [[downgrade attack]]s between the offered configurations, with both IKEv1 and IKEv2.<ref name="ike-downgrade">{{Cite web | url=https://eprint.iacr.org/2016/072.pdf | title=Downgrade Resilience in Key-Exchange Protocols | first1=Karthikeyan | last1=Bhargavan | first2=Christina | last2=Brzuska | first3=Cédric | last3=Fournet | first4=Markulf | last4=Kohlweiss | first5=Santiago | last5=Zanella-Béguelin | first6=Matthew | last6=Green | date=January 2016 }}</ref>  This can be avoided by careful segregation of client systems onto multiple service access points with stricter configurations.

Both versions of the IKE standard are susceptible to an offline [[dictionary attack]] when a low entropy password is used. For the IKEv1 this is true for main mode and aggressive mode.<ref>{{Cite web|url=http://skysrv.pha.jhu.edu/~jpliam/ima/xauth/|title=Authentication Vulnerabilities in IKE and Xauth with Weak Pre-Shared Secrets|last=Pliam|first=John|date=2 October 1999|website=Johns Hopkins University|url-status=live|archive-url=https://web.archive.org/web/20020610050311/http://www.ima.umn.edu/~pliam/xauth/|archive-date=10 June 2002|access-date=5 February 2020}}</ref><ref>{{Cite web|url=http://blogs.cisco.com/security/great-cipher-but-where-did-you-get-that-key/|title=Great Cipher, But Where Did You Get That Key|last=McGrew|first=David|date=5 July 2011|website=Cisco Blog|url-status=dead|archive-url=https://web.archive.org/web/20110709020412/http://blogs.cisco.com/security/great-cipher-but-where-did-you-get-that-key/|archive-date=9 July 2011|access-date=11 February 2020}}</ref><ref>{{Cite book|url=https://www.usenix.org/conference/usenixsecurity18/presentation/felsch|title=The Dangers of Key Reuse: Practical Attacks on IPsec IKE|last=Felsch|first=Dennis|date=August 2018|website=27th USENIX Security Symposium|isbn=9781939133045 |access-date=11 February 2020}}</ref>