crypto/hmac: Allow to build hmac over multiple qcrypto_gnutls_hmac_bytes[v] calls

If the buffers that should be considered for building the hmac are not
available at the same time, the current API is unsuitable. Extend it so
that passing a NULL pointer as result_len is used as indicator that
further buffers will be passed in succeeding calls to
qcrypto_gnutls_hmac_bytes[v].

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <2d3539c247a6c323491a3821f0e5b6fc382a4686.1756706188.git.jan.kiszka@siemens.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/crypto/hmac.h b/include/crypto/hmac.h
index da8a1e3ceb..af3d5f8feb 100644
--- a/include/crypto/hmac.h
+++ b/include/crypto/hmac.h
@@ -90,6 +90,12 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC(QCryptoHmac, qcrypto_hmac_free)
  * The memory referenced in @result must be released with a call
  * to g_free() when no longer required by the caller.
  *
+ * If @result_len is set to a NULL pointer, no result will be returned, and
+ * the hmac object can be used for further invocations of qcrypto_hmac_bytes()
+ * or qcrypto_hmac_bytesv() until a non-NULL pointer is provided. This allows
+ * to build the hmac across memory regions that are not available at the same
+ * time.
+ *
  * Returns:
  *  0 on success, -1 on error
  */
@@ -123,6 +129,12 @@ int qcrypto_hmac_bytesv(QCryptoHmac *hmac,
  * The memory referenced in @result must be released with a call
  * to g_free() when no longer required by the caller.
  *
+ * If @result_len is set to a NULL pointer, no result will be returned, and
+ * the hmac object can be used for further invocations of qcrypto_hmac_bytes()
+ * or qcrypto_hmac_bytesv() until a non-NULL pointer is provided. This allows
+ * to build the hmac across memory regions that are not available at the same
+ * time.
+ *
  * Returns:
  *  0 on success, -1 on error
  */