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fix: wc_SignatureVerify/Generate allow empty messages #10253

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fix: wc_SignatureVerify/Generate allow empty messages #10253

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11 changes: 7 additions & 4 deletions wolfcrypt/src/signature.c
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Original file line number Diff line number Diff line change
Expand Up @@ -324,8 +324,10 @@ int wc_SignatureVerify(
byte hash_data[MAX_DER_DIGEST_SZ];
#endif

/* Check arguments */
if (data == NULL || data_len == 0 ||
/* Check arguments.
* data may be NULL when data_len is 0 (empty message is valid —
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Copilot AI Apr 17, 2026

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These new comments introduce a non-ASCII em dash character (—). This can cause portability/encoding issues for toolchains that assume ASCII-only C sources or have strict source-charset settings. Consider replacing it with an ASCII sequence like '-' or '--' to avoid build problems in constrained environments.

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* data may be NULL when data_len is 0 (empty message is valid —
* data may be NULL when data_len is 0 (empty message is valid -

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* the hash of an empty string is well-defined). */
if ((data == NULL && data_len > 0) ||
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Copilot AI Apr 17, 2026

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This change introduces new behavior (allowing empty-message verify). To prevent regressions, add an automated regression test that verifies a known-good signature over an empty message (including the data == NULL, data_len == 0 case), matching the reported Wycheproof vectors.

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sig == NULL || sig_len == 0 ||
key == NULL || key_len == 0) {
return BAD_FUNC_ARG;
Expand Down Expand Up @@ -523,8 +525,9 @@ int wc_SignatureGenerate_ex(
byte hash_data[MAX_DER_DIGEST_SZ];
#endif

/* Check arguments */
if (data == NULL || data_len == 0 ||
/* Check arguments.
* data may be NULL when data_len is 0 (signing an empty message). */
if ((data == NULL && data_len > 0) ||
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Copilot AI Apr 17, 2026

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This change introduces new behavior (allowing empty-message signing). Add an automated regression test that signs an empty message (including data == NULL, data_len == 0) and then verifies it, ensuring the previous BAD_FUNC_ARG behavior does not return.

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sig == NULL || sig_len == NULL || *sig_len == 0 ||
key == NULL || key_len == 0) {
return BAD_FUNC_ARG;
Expand Down
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