Makefile: discuss SHAttered in *_SHA{1,256} discussion

avar · ttaylorr · commit d00fa5528b44 · 2022-11-07T22:11:51.000-05:00
Let's mention the SHAttered attack and more generally why we use the
sha1collisiondetection backend by default, and note that for SHA-256
the user should feel free to pick any of the supported backends as far
as hashing security is concerned.

Signed-off-by: Ævar Arnfjörð Bjarmason &lt;avarab@gmail.com&gt;
Signed-off-by: Taylor Blau &lt;me@ttaylorr.com&gt;
diff --git a/Makefile b/Makefile
@@ -481,6 +481,17 @@ include shared.mak
 #
 # === SHA-1 backend ===
 #
+# ==== Security ====
+#
+# Due to the SHAttered (https://shattered.io) attack vector on SHA-1
+# it's strongly recommended to use the sha1collisiondetection
+# counter-cryptanalysis library for SHA-1 hashing.
+#
+# If you know that you can trust the repository contents, or where
+# potential SHA-1 attacks are otherwise mitigated the other backends
+# listed in "SHA-1 implementations" are faster than
+# sha1collisiondetection.
+#
 # ==== Default SHA-1 backend ====
 #
 # If no *_SHA1 backend is picked, the first supported one listed in
@@ -525,6 +536,11 @@ include shared.mak
 #
 # === SHA-256 backend ===
 #
+# ==== Security ====
+#
+# Unlike SHA-1 the SHA-256 algorithm does not suffer from any known
+# vulnerabilities, so any implementation will do.
+#
 # ==== SHA-256 implementations ====
 #
 # Define OPENSSL_SHA256 to use the SHA-256 routines in OpenSSL.

Original file line number	Diff line number	Diff line change
`@@ -481,6 +481,17 @@ include shared.mak`
`481`	`481`	`#`
`482`	`482`	`# === SHA-1 backend ===`
`483`	`483`	`#`
	`484`	`+# ==== Security ====`
	`485`	`+#`
	`486`	`+# Due to the SHAttered (https://shattered.io) attack vector on SHA-1`
	`487`	`+# it's strongly recommended to use the sha1collisiondetection`
	`488`	`+# counter-cryptanalysis library for SHA-1 hashing.`
	`489`	`+#`
	`490`	`+# If you know that you can trust the repository contents, or where`
	`491`	`+# potential SHA-1 attacks are otherwise mitigated the other backends`
	`492`	`+# listed in "SHA-1 implementations" are faster than`
	`493`	`+# sha1collisiondetection.`
	`494`	`+#`
`484`	`495`	`# ==== Default SHA-1 backend ====`
`485`	`496`	`#`
`486`	`497`	`# If no *_SHA1 backend is picked, the first supported one listed in`
`@@ -525,6 +536,11 @@ include shared.mak`
`525`	`536`	`#`
`526`	`537`	`# === SHA-256 backend ===`
`527`	`538`	`#`
	`539`	`+# ==== Security ====`
	`540`	`+#`
	`541`	`+# Unlike SHA-1 the SHA-256 algorithm does not suffer from any known`
	`542`	`+# vulnerabilities, so any implementation will do.`
	`543`	`+#`
`528`	`544`	`# ==== SHA-256 implementations ====`
`529`	`545`	`#`
`530`	`546`	`# Define OPENSSL_SHA256 to use the SHA-256 routines in OpenSSL.`