From 99bd1df99b2ada05877f36f85ff2f7f37e176fd6 Mon Sep 17 00:00:00 2001
From: Adam Langley <agl@chromium.org>
Date: Thu, 3 Apr 2025 09:57:44 -0700
Subject: [PATCH] Remove MAC truncation from FIPS interface.

This is only valid in ACVP if the truncation occurs within the FIPS
module. But that's not a useful service: the caller can always discard a
few bytes and is better positioned to do so.

Change-Id: Id5e6459c9fa6d8b1b8f7a398feab6c4816adf8ab
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/78247
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: Adam Langley <agl@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
---
 .../acvp/acvptool/subprocess/hmac.go          |  6 ++--
 .../acvp/modulewrapper/modulewrapper.cc       | 34 +++++--------------
 2 files changed, 12 insertions(+), 28 deletions(-)

diff --git a/util/fipstools/acvp/acvptool/subprocess/hmac.go b/util/fipstools/acvp/acvptool/subprocess/hmac.go
index 3273f3ce9..e4d5e405c 100644
--- a/util/fipstools/acvp/acvptool/subprocess/hmac.go
+++ b/util/fipstools/acvp/acvptool/subprocess/hmac.go
@@ -119,14 +119,14 @@ func (h *hmacPrimitive) Process(vectorSet []byte, m Transactable) (any, error) {
 			}
 
 			m.TransactAsync(h.algo, 1, [][]byte{msg, key}, func(result [][]byte) error {
-				if l := len(result[0]); l < outBytes {
-					return fmt.Errorf("HMAC result too short: %d bytes but wanted %d", l, outBytes)
+				if l := len(result[0]); l != outBytes {
+					return fmt.Errorf("incorrect HMAC length: %d bytes but wanted %d", l, outBytes)
 				}
 
 				// https://pages.nist.gov/ACVP/draft-fussell-acvp-mac.html#name-test-vectors
 				response.Tests = append(response.Tests, hmacTestResponse{
 					ID:     test.ID,
-					MACHex: hex.EncodeToString(result[0][:outBytes]),
+					MACHex: hex.EncodeToString(result[0]),
 				})
 				return nil
 			})
diff --git a/util/fipstools/acvp/modulewrapper/modulewrapper.cc b/util/fipstools/acvp/modulewrapper/modulewrapper.cc
index 7f4d9fa0d..018aceb4b 100644
--- a/util/fipstools/acvp/modulewrapper/modulewrapper.cc
+++ b/util/fipstools/acvp/modulewrapper/modulewrapper.cc
@@ -442,9 +442,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 160, "increment": 8
-        }]
+        "macLen": [160]
       },
       {
         "algorithm": "HMAC-SHA2-224",
@@ -452,9 +450,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 224, "increment": 8
-        }]
+        "macLen": [224]
       },
       {
         "algorithm": "HMAC-SHA2-256",
@@ -462,9 +458,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 256, "increment": 8
-        }]
+        "macLen": [256]
       },
       {
         "algorithm": "HMAC-SHA2-384",
@@ -472,9 +466,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 384, "increment": 8
-        }]
+        "macLen": [384]
       },
       {
         "algorithm": "HMAC-SHA2-512",
@@ -482,9 +474,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 512, "increment": 8
-        }]
+        "macLen": [512]
       },
       {
         "algorithm": "HMAC-SHA2-512/256",
@@ -492,9 +482,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
         "keyLen": [{
           "min": 8, "max": 524288, "increment": 8
         }],
-        "macLen": [{
-          "min": 32, "max": 256, "increment": 8
-        }]
+        "macLen": [256]
       },
       {
         "algorithm": "ctrDRBG",
@@ -848,11 +836,7 @@ static bool GetConfig(const Span<const uint8_t> args[],
             "increment": 8
           }],
           "keyLen": [128, 256],
-          "macLen": [{
-            "min": 8,
-            "max": 128,
-            "increment": 8
-          }]
+          "macLen": [128]
         }]
       },
       {
@@ -1966,11 +1950,11 @@ static bool CMAC_AES(const Span<const uint8_t> args[],
     return false;
   }
   memcpy(&mac_len, args[0].data(), sizeof(mac_len));
-  if (mac_len > sizeof(mac)) {
+  if (mac_len != sizeof(mac)) {
     return false;
   }
 
-  return write_reply({Span<const uint8_t>(mac, mac_len)});
+  return write_reply({Span<const uint8_t>(mac, sizeof(mac))});
 }
 
 static bool CMAC_AESVerify(const Span<const uint8_t> args[],