Add documentation notes about the required size of the signature buffers
diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 91950f9..1364275 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -416,6 +416,10 @@
*
* \note For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
* For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
+ *
+ * \note In order to ensure enough space for the signature, the
+ * \p sig buffer size must be of at least
+ * `max(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)` bytes.
*/
int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
@@ -430,6 +434,10 @@
* \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
* operations. For RSA, same as \c mbedtls_pk_sign().
*
+ * \note In order to ensure enough space for the signature, the
+ * \p sig buffer size must be of at least
+ * `max(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)` bytes.
+ *
* \param ctx The PK context to use. It must have been set up
* with a private key.
* \param md_alg Hash algorithm used (see notes)
diff --git a/include/mbedtls/rsa.h b/include/mbedtls/rsa.h
index 906c427..cba692b 100644
--- a/include/mbedtls/rsa.h
+++ b/include/mbedtls/rsa.h
@@ -904,7 +904,8 @@
* the size of the hash corresponding to \p md_alg.
* \param sig The buffer to hold the signature. This must be a writable
* buffer of length \c ctx->len Bytes. For example, \c 256 Bytes
- * for an 2048-bit RSA modulus.
+ * for an 2048-bit RSA modulus. A buffer length of
+ * #MBEDTLS_MPI_MAX_SIZE is always safe.
*
* \return \c 0 if the signing operation was successful.
* \return An \c MBEDTLS_ERR_RSA_XXX error code on failure.
@@ -951,7 +952,8 @@
* the size of the hash corresponding to \p md_alg.
* \param sig The buffer to hold the signature. This must be a writable
* buffer of length \c ctx->len Bytes. For example, \c 256 Bytes
- * for an 2048-bit RSA modulus.
+ * for an 2048-bit RSA modulus. A buffer length of
+ * #MBEDTLS_MPI_MAX_SIZE is always safe.
*
* \return \c 0 if the signing operation was successful.
* \return An \c MBEDTLS_ERR_RSA_XXX error code on failure.
@@ -1012,7 +1014,8 @@
* the size of the hash corresponding to \p md_alg.
* \param sig The buffer to hold the signature. This must be a writable
* buffer of length \c ctx->len Bytes. For example, \c 256 Bytes
- * for an 2048-bit RSA modulus.
+ * for an 2048-bit RSA modulus. A buffer length of
+ * #MBEDTLS_MPI_MAX_SIZE is always safe.
*
* \return \c 0 if the signing operation was successful.
* \return An \c MBEDTLS_ERR_RSA_XXX error code on failure.