Re: [Cfrg] AES-GCM-SIV security of the additional data
"Blumenthal, Uri - 0553 - MITLL" <uri@ll.mit.edu> Fri, 24 June 2016 18:03 UTC
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From: "Blumenthal, Uri - 0553 - MITLL" <uri@ll.mit.edu>
To: Daniel Bleichenbacher <bleichen@google.com>
Thread-Topic: [Cfrg] AES-GCM-SIV security of the additional data
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Date: Fri, 24 Jun 2016 18:03:13 +0000
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Subject: Re: [Cfrg] AES-GCM-SIV security of the additional data
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> On Fri, Jun 24, 2016 at 3:08 PM, Blumenthal, Uri - 0553 - MITLL > <uri@ll.mit.edu> wrote: >> What is the probability of a sender (accidentally?) generating a key that >> results in H being 0? > > Random key generation is not my concern. My concern is a sender choosing a key > on purpose in such a way that > he does not have to authenticate additional data. If our threat model is malicious sender that may try to “disown” his message or deliberately allow somebody else to modify it – that same malicious sender could covertly share his key and claim that adversaries guessed it (highly improbable but not impossible). > The typical assumption is that if an integrity check passes then the sender is > aware of the plaintext. Should this also be the case for the additional data? Probably not, if/when the sender deliberately makes it not so. ??? P.S. How easy is it to find such a key [that makes H = 0]? >> From: Daniel Bleichenbacher >> Sent: Friday, June 24, 2016 07:35 >> To: cfrg@ietf.org >> Subject: [Cfrg] AES-GCM-SIV security of the additional data >> >> >> I'm wondering what can or should be expected about the security of the >> additional data. >> >> In particular, I'm considering the following scenario: >> >> Sender and receiver share a secret S. >> The sender knows the public key of the receiver and the receiver of course >> knows the private key. >> They use a hybrid encryption as follows: >> >> The sender chooses a new AES-GCM-SIV key, encrypts his message >> and includes S as additional data. The AES-GCM-SIV key is wrapped with >> the receivers public key and the wrapped key and ciphertext are sent to the >> receiver. >> >> Here an attacker can use that AES-GCM-SIV allows to select a key such that >> the >> element H used for POLYVAL is 0. In this case it would not be necessary for >> the sender >> to know S to construct a ciphertext that validates. >> A similar attack using AES-GCM seems much harder since the value H for the >> GHASH >> is obtained by encrypting 0 and thus I'm not aware of a way to do the same >> thing here. >> >> The attack does of course not violate any of the guarantees claimed. >> However, in the industry lots of ad hoc protocols are designed without proper >> security reductions and hence it seems a bit scary to me to allow this kind >> of "weak" keys. And since abuse resistance is >> one of the goals it might be a good idea to avoid such type of abuses. >> >> >
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Paterson, Kenny
- Re: [Cfrg] AES-GCM-SIV security of the additional… Adam Langley
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Aaron Zauner
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Gueron, Shay
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Aaron Zauner
- Re: [Cfrg] AES-GCM-SIV security of the additional… Gueron, Shay
- Re: [Cfrg] AES-GCM-SIV security of the additional… Paterson, Kenny
- Re: [Cfrg] AES-GCM-SIV security of the additional… Blumenthal, Uri - 0553 - MITLL
- Re: [Cfrg] AES-GCM-SIV security of the additional… Jim Schaad
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Blumenthal, Uri - 0553 - MITLL
- Re: [Cfrg] AES-GCM-SIV security of the additional… Blumenthal, Uri - 0553 - MITLL
- [Cfrg] AES-GCM-SIV with a new key hierarchy Gueron, Shay
- Re: [Cfrg] AES-GCM-SIV security of the additional… Gueron, Shay
- Re: [Cfrg] AES-GCM-SIV security of the additional… Daniel Bleichenbacher
- Re: [Cfrg] AES-GCM-SIV security of the additional… Paterson, Kenny
- Re: [Cfrg] AES-GCM-SIV security of the additional… Antonio Sanso
- Re: [Cfrg] AES-GCM-SIV security of the additional… Paterson, Kenny
- Re: [Cfrg] AES-GCM-SIV security of the additional… Blumenthal, Uri - 0553 - MITLL
- [Cfrg] AES-GCM-SIV security of the additional data Daniel Bleichenbacher
- Re: [Cfrg] AES-GCM-SIV security of the additional… Daniel Bleichenbacher
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Dan Harkins
- Re: [Cfrg] AES-GCM-SIV with a new key hierarchy Shay Gueron