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CMS decryption with kuznyechik-ctr-acpkm produces corrupted plaintext for payloads larger than 4096 bytes. #529
Description
Problem
CMS decryption with kuznyechik-ctr-acpkm produces corrupted plaintext for payloads larger than 4096 bytes.
The command exits successfully, but the decrypted output is incorrect. In the reproducer below, the 1024-byte file decrypts correctly, while the 8192-byte file differs from the original starting at byte 4097.
Reproducer
Assumption: OpenSSL with GOST engine support is already installed and configured.
tmpdir="$(mktemp -d)"
cd "$tmpdir"Generate a fresh GOST private key and a self-signed certificate.
openssl req -x509 \
-newkey gost2012_256 \
-pkeyopt paramset:A \
-keyout key.pem \
-out cert.pem \
-nodes \
-subj "/CN=acpkm-repro" \
-days 1Create two plaintext files: one below the 4096-byte boundary and one above it.
head -c 1024 /dev/zero > text_1024.bin
head -c 8192 /dev/zero > text_8192.binEncrypt both files with CMS using Kuznyechik CTR-ACPKM.
openssl cms -encrypt \
-binary \
-outform DER \
-kuznyechik-ctr-acpkm \
-in text_1024.bin \
-out text_1024.bin.p7e \
cert.pem
openssl cms -encrypt \
-binary \
-outform DER \
-kuznyechik-ctr-acpkm \
-in text_8192.bin \
-out text_8192.bin.p7e \
cert.pemDecrypt both CMS files.
openssl cms -decrypt \
-binary \
-inform DER \
-inkey key.pem \
-in text_1024.bin.p7e \
-out decrypted_1024.bin
openssl cms -decrypt \
-binary \
-inform DER \
-inkey key.pem \
-in text_8192.bin.p7e \
-out decrypted_8192.binCompare original and decrypted files.
sha256sum text_1024.bin decrypted_1024.bin
sha256sum text_8192.bin decrypted_8192.bin
cmp -s text_1024.bin decrypted_1024.bin && echo "1024 OK"
cmp -s text_8192.bin decrypted_8192.bin && echo "8192 OK" || echo "8192 corrupted"Show the first corrupted bytes.
cmp -l text_8192.bin decrypted_8192.bin | headExpected result: both decrypted files match the original files.
Actual result: the 1024-byte file matches, but the 8192-byte file does not. The first difference starts at byte 4097.
I created pr which fixes this issue: #528
Activity
rostislaved commentedon Sep 25, 2026
@chipitsine привет! Получится посмотреть?
chipitsine commentedon Sep 25, 2026
надо бы. знатный баг
chipitsine commentedon Oct 11, 2026
немного поправил проверку граничных условий.