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From 3ea2a5a026e73d81cd9a3e9bbd4300c433004bfa Mon Sep 17 00:00:00 2001
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From: Mathy Vanhoef <mathy.vanhoef@nyu.edu>
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Date: Wed, 5 Jun 2019 19:21:06 +0000
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Subject: [PATCH] EAP-pwd: fix side-channel leak where 1 in 2018 handshakes
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fail
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Previously the Hunting and Pecking algorithm of EAP-pwd aborted when
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more than 10 iterations are needed. Every iteration has a 50% chance
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of finding the password element. This means one in every 2048 handshakes
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will fail, in which case an error frame is sent to the client. This
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event leaks information that can be abused in an offline password
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brute-force attack. More precisely, the adversary learns that all 10
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iterations failed for the given random EAP-pwd token. Using the same
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techniques as in the Dragonblood attack, this can be used to brute-force
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the password.
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This patch fixes the above issue by executing enough iterations such that
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the password element is always found eventually.
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Note that timing and cache leaks remain a risk against the current
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implementation of EAP-pwd.
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---
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src/modules/rlm_eap/types/rlm_eap_pwd/eap_pwd.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/modules/rlm_eap/types/rlm_eap_pwd/eap_pwd.c b/src/modules/rlm_eap/types/rlm_eap_pwd/eap_pwd.c
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index c54f08c030..d94851c3aa 100644
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--- a/src/modules/rlm_eap/types/rlm_eap_pwd/eap_pwd.c
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+++ b/src/modules/rlm_eap/types/rlm_eap_pwd/eap_pwd.c
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@@ -192,7 +192,7 @@ int compute_password_element (pwd_session_t *session, uint16_t grp_num,
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}
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ctr = 0;
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while (1) {
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- if (ctr > 10) {
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+ if (ctr > 100) {
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DEBUG("unable to find random point on curve for group %d, something's fishy", grp_num);
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goto fail;
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}
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