diff --git a/include/qpdf/QPDF.hh b/include/qpdf/QPDF.hh
index 89fdf81..dba648b 100644
--- a/include/qpdf/QPDF.hh
+++ b/include/qpdf/QPDF.hh
@@ -438,6 +438,9 @@ class QPDF
     // Encryption support
 
     enum encryption_method_e { e_none, e_unknown, e_rc4, e_aes, e_aesv3 };
+
+    // To be removed from the public API in qpdf 13. See
+    // <https:manual.qpdf.org/release-notes.html#r12-3-0-deprecate>.
     class EncryptionData
     {
       public:
@@ -558,8 +561,10 @@ class QPDF
         bool use_aes,
         int encryption_V,
         int encryption_R);
-    QPDF_DLL
-    static std::string
+
+    // To be removed in qpdf 13. See <https:manual.qpdf.org/release-notes.html#r12-3-0-deprecate>.
+    [[deprecated("to be removed in qpdf 13")]]
+    QPDF_DLL static std::string
     compute_encryption_key(std::string const& password, EncryptionData const& data);
 
     QPDF_DLL
diff --git a/manual/release-notes.rst b/manual/release-notes.rst
index a68d42f..72c8e93 100644
--- a/manual/release-notes.rst
+++ b/manual/release-notes.rst
@@ -65,6 +65,15 @@ more detail.
 
   - Other changes
 
+.. _r12-3-0-deprecate:
+
+    - The following are believed to be not in use and have been deprecated.
+      If you are relying on them please open a ticket_.
+
+      - QPDF::compute_encryption_key
+      - All QPDF::EncryptionData methods. These methods are not exported in the
+        shared library and are only useable in statically linked programs.
+
     - Setting :qpdf:ref:`--compress-streams` to ``n`` or
       ``QPDFWriter::setCompressStreams(false)`` no longer automatically
       causes the outputfile to be decrypted. Set :qpdf:ref:`--decrypt` if this