1 files changed, 62 insertions, 0 deletions
diff --git a/tests/src/asn1_helpers.c b/tests/src/asn1_helpers.c
new file mode 100644
index 00000000000..c8df1995e31
--- /dev/null
+++ b/tests/src/asn1_helpers.c
@@ -0,0 +1,62 @@
+/** \file asn1_helpers.c
+ *
+ * \brief Helper functions for tests that manipulate ASN.1 data.
+ */
+
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+#include <test/helpers.h>
+#include <test/macros.h>
+
+#if defined(MBEDTLS_ASN1_PARSE_C)
+
+#include <mbedtls/asn1.h>
+
+int mbedtls_test_asn1_skip_integer(unsigned char **p, const unsigned char *end,
+                                   size_t min_bits, size_t max_bits,
+                                   int must_be_odd)
+{
+    size_t len;
+    size_t actual_bits;
+    unsigned char msb;
+    TEST_EQUAL(mbedtls_asn1_get_tag(p, end, &len,
+                                    MBEDTLS_ASN1_INTEGER),
+               0);
+
+    /* Check if the retrieved length doesn't extend the actual buffer's size.
+     * It is assumed here, that end >= p, which validates casting to size_t. */
+    TEST_ASSERT(len <= (size_t) (end - *p));
+
+    /* Tolerate a slight departure from DER encoding:
+     * - 0 may be represented by an empty string or a 1-byte string.
+     * - The sign bit may be used as a value bit. */
+    if ((len == 1 && (*p)[0] == 0) ||
+        (len > 1 && (*p)[0] == 0 && ((*p)[1] & 0x80) != 0)) {
+        ++(*p);
+        --len;
+    }
+    if (min_bits == 0 && len == 0) {
+        return 1;
+    }
+    msb = (*p)[0];
+    TEST_ASSERT(msb != 0);
+    actual_bits = 8 * (len - 1);
+    while (msb != 0) {
+        msb >>= 1;
+        ++actual_bits;
+    }
+    TEST_ASSERT(actual_bits >= min_bits);
+    TEST_ASSERT(actual_bits <= max_bits);
+    if (must_be_odd) {
+        TEST_ASSERT(((*p)[len-1] & 1) != 0);
+    }
+    *p += len;
+    return 1;
+exit:
+    return 0;
+}
+
+#endif /* MBEDTLS_ASN1_PARSE_C */