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From 998065599c66055dcffa1ef1ddebb947ccd68248 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
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Date: Thu, 9 Feb 2017 09:45:01 +0100
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Subject: DH: Ensure that generated secret occupies the same number of bytes as
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prime.
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https://bugzilla.gnome.org/show_bug.cgi?id=778357
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---
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egg/egg-dh.c | 15 +++++++++++----
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1 file changed, 11 insertions(+), 4 deletions(-)
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diff --git a/egg/egg-dh.c b/egg/egg-dh.c
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index e869c99..b190488 100644
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--- a/egg/egg-dh.c
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+++ b/egg/egg-dh.c
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@@ -314,6 +314,7 @@ egg_dh_gen_secret (gcry_mpi_t peer, gcry_mpi_t priv,
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{
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gcry_error_t gcry;
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guchar *value;
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+ gsize n_prime;
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gsize n_value;
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gcry_mpi_t k;
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gint bits;
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@@ -330,19 +331,25 @@ egg_dh_gen_secret (gcry_mpi_t peer, gcry_mpi_t priv,
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gcry_mpi_powm (k, peer, priv, prime);
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/* Write out the secret */
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- gcry = gcry_mpi_print (GCRYMPI_FMT_USG, NULL, 0, &n_value, k);
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+ gcry = gcry_mpi_print (GCRYMPI_FMT_USG, NULL, 0, &n_prime, prime);
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g_return_val_if_fail (gcry == 0, NULL);
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- value = egg_secure_alloc (n_value);
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- gcry = gcry_mpi_print (GCRYMPI_FMT_USG, value, n_value, &n_value, k);
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+ value = egg_secure_alloc (n_prime);
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+ gcry = gcry_mpi_print (GCRYMPI_FMT_USG, value, n_prime, &n_value, k);
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g_return_val_if_fail (gcry == 0, NULL);
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+ /* Pad the secret with zero bytes to match length of prime in bytes. */
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+ if (n_value < n_prime) {
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+ memmove (value + (n_prime - n_value), value, n_value);
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+ memset (value, 0, (n_prime - n_value));
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+ }
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+
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#if DEBUG_DH_SECRET
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g_printerr ("DH SECRET: ");
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gcry_mpi_dump (k);
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#endif
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gcry_mpi_release (k);
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- *bytes = n_value;
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+ *bytes = n_prime;
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#if DEBUG_DH_SECRET
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gcry_mpi_scan (&k, GCRYMPI_FMT_USG, value, bytes, NULL);
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--
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cgit v0.12
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