cksum: allow -a {blake2b,sha2,sha3} --check to work on base64

* NEWS: Mention the bug.
* src/digest.c (split_3): Check that the base64 digest matches the
length supported by the algorithm.
(digest_check): Check that the read digest matches the base64 length of
the algorithm's digest. The previous condition would not work for
'cksum -a blake2b -l 8 ...'.
* tests/cksum/cksum-base64-untagged.sh: New file.
* tests/local.mk (all_tests): Add the new test.

2 files changed, 51 insertions, 0 deletions

diff --git a/tests/cksum/cksum-base64-untagged.sh b/tests/cksum/cksum-base64-untagged.sh
new file mode 100755
index 000000000..14e194289
--- /dev/null
+++ b/tests/cksum/cksum-base64-untagged.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+# Test that cksum can guess the digest length from base64 checksums.
+
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ cksum
+
+echo 'test input' > inp
+echo 'inp: OK' > expout
+echo 'cksum: truncated: no properly formatted checksum lines found' > experr
+
+for algorithm in sha2 sha3; do
+  for length in 224 256 384 512; do
+    # Create files with base64 checksums in the untagged format.
+    cksum -a $algorithm --length $length --base64 --untagged inp \
+      > check || fail=1
+    # Check that the length can be determined from the base64 checksum.
+    cksum -a $algorithm --check check > out || fail=1
+    compare expout out || fail=1
+    # Check that only valid lengths are supported.
+    sed 's|[a-zA-Z0-9+/=]  inp$|  inp|g' check > truncated || fail=1
+    returns_ 1 cksum -a $algorithm --check truncated 2> err || fail=1
+    compare experr err || fail=1
+  done
+done
+
+for length in 8 216 224 232 248 256 264 376 384 392 504 512; do
+  # Create files with base64 checksums in the untagged format.
+  cksum -a blake2b --length $length --base64 --untagged inp \
+    > check || fail=1
+  # Check that the length can be determined from the base64 checksum.
+  cksum -a blake2b --check check > out || fail=1
+  compare expout out || fail=1
+done
+
+Exit $fail
diff --git a/tests/local.mk b/tests/local.mk
index 19bc194fb..52184b7ac 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -305,6 +305,7 @@ all_tests =					\
   tests/cksum/cksum-a.sh			\
   tests/cksum/cksum-c.sh			\
   tests/cksum/cksum-base64.pl			\
+  tests/cksum/cksum-base64-untagged.sh		\
   tests/cksum/cksum-raw.sh			\
   tests/misc/comm.pl				\
   tests/csplit/csplit.sh			\