854fe94ab1
* Update buildroot to 2021.02.6 * Renew buildroot-patches This makes sure that docker-proxy gets bumped to the latest Docker version as well.
39 lines
1.4 KiB
Diff
39 lines
1.4 KiB
Diff
From 9a23e4e3bc3966340531f2ff608fa9d33b5185a2 Mon Sep 17 00:00:00 2001
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From: Jack Lloyd <jack@randombit.net>
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Date: Tue, 3 Aug 2021 18:20:29 -0400
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Subject: [PATCH] Avoid using short exponents with ElGamal
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Some off-brand PGP implementation generates keys where p - 1 is
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smooth, as a result short exponents can leak enough information about
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k to allow decryption.
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Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
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[Peter: Drop tests, CVE-2021-40529]
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---
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src/lib/pubkey/elgamal/elgamal.cpp | 8 +++-
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1 file changed, 1 insertions(+), 1 deletions(-)
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diff --git a/src/lib/pubkey/elgamal/elgamal.cpp b/src/lib/pubkey/elgamal/elgamal.cpp
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index b3ec6df2c..0e33c2ca5 100644
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--- a/src/lib/pubkey/elgamal/elgamal.cpp
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+++ b/src/lib/pubkey/elgamal/elgamal.cpp
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@@ -113,8 +113,12 @@ ElGamal_Encryption_Operation::raw_encrypt(const uint8_t msg[], size_t msg_len,
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if(m >= m_group.get_p())
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throw Invalid_Argument("ElGamal encryption: Input is too large");
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- const size_t k_bits = m_group.exponent_bits();
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- const BigInt k(rng, k_bits);
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+ /*
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+ Some ElGamal implementations foolishly use prime fields where p - 1 is
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+ smooth, as a result it is unsafe to use short exponents.
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+ */
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+ const size_t k_bits = m_group.p_bits() - 1;
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+ const BigInt k(rng, k_bits, false);
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const BigInt a = m_group.power_g_p(k, k_bits);
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const BigInt b = m_group.multiply_mod_p(m, monty_execute(*m_monty_y_p, k, k_bits));
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-
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--
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2.20.1
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