diff --git a/tests/scripts/set_psa_test_dependencies.py b/tests/scripts/set_psa_test_dependencies.py
index 36f0eae..96dd94b 100755
--- a/tests/scripts/set_psa_test_dependencies.py
+++ b/tests/scripts/set_psa_test_dependencies.py
@@ -19,8 +19,20 @@
 # limitations under the License.
 
 import os
+import re
 import sys
 
+def updated_dependencies(file_name, function_name, arguments, dependencies):
+    """Rework the list of dependencies into PSA_WANT_xxx.
+
+    Remove classic crypto dependencies such as MBEDTLS_RSA_C,
+    MBEDTLS_PKCS1_V15, etc.
+
+    Add systematic PSA_WANT_xxx dependencies based on the called function and
+    its arguments, replacing existing PSA_WANT_xxx dependencies.
+    """
+    return dependencies #TODO
+
 def process_data_stanza(stanza, file_name, test_case_number):
     """Update PSA crypto dependencies in one Mbed TLS test case.
 
@@ -29,7 +41,48 @@
     a new stanza with an updated dependency line, preserving everything else
     (description, comments, arguments, etc.).
     """
-    #TODO: not implemented yet
+    if not stanza.lstrip('\n'):
+        # Just blank lines
+        return stanza
+    # Expect 2 or 3 non-comment lines: description, optional dependencies,
+    # function-and-arguments.
+    content_matches = list(re.finditer(r'^[\t ]*([^\t #].*)$', stanza, re.M))
+    if len(content_matches) < 2:
+        raise Exception('Not enough content lines in paragraph {} in {}'
+                        .format(test_case_number, file_name))
+    if len(content_matches) > 3:
+        raise Exception('Too many content lines in paragraph {} in {}'
+                        .format(test_case_number, file_name))
+    arguments = content_matches[-1].group(0).split(':')
+    function_name = arguments.pop(0)
+    if len(content_matches) == 2:
+        # Insert a line for the dependencies. If it turns out that there are
+        # no dependencies, we'll remove that empty line below.
+        dependencies_location = content_matches[-1].start()
+        text_before = stanza[:dependencies_location]
+        text_after = '\n' + stanza[dependencies_location:]
+        old_dependencies = []
+        dependencies_leader = 'depends_on:'
+    else:
+        dependencies_match = content_matches[-2]
+        text_before = stanza[:dependencies_match.start()]
+        text_after = stanza[dependencies_match.end():]
+        old_dependencies = dependencies_match.group(0).split(':')
+        dependencies_leader = old_dependencies.pop(0) + ':'
+        if dependencies_leader != 'depends_on:':
+            raise Exception('Next-to-last line does not start with "depends_on:"'
+                            ' in paragraph {} in {}'
+                            .format(test_case_number, file_name))
+    new_dependencies = updated_dependencies(file_name, function_name, arguments,
+                                            old_dependencies)
+    if new_dependencies:
+        stanza = (text_before +
+                  dependencies_leader + ':'.join(new_dependencies) +
+                  text_after)
+    else:
+        # The dependencies have become empty. Remove the depends_on: line.
+        assert text_after[0] == '\n'
+        stanza = text_before + text_after[1:]
     return stanza
 
 def process_data_file(file_name, old_content):