Import mbedtls-3.6.0

Imports Mbed TLS 3.6.0 from https://github.com/Mbed-TLS/mbedtls.git
tags mbedtls-3.6.0, v3.6.0

Files that are not needed are removed:

cd lib/libmbedtls
rm -rf mbedtls
cp -R path/to/mbedtls-3.6.0/mbedtls .
cd mbedtls
rm CMakeLists.txt DartConfiguration.tcl Makefile
rm .gitignore .travis.yml .pylintrc .globalrc .mypy.ini BRANCHES.md
rm include/.gitignore include/CMakeLists.txt library/.gitignore
rm library/CMakeLists.txt library/Makefile
rm -r cmake
rm -rf .git .github doxygen configs programs scripts tests visualc
rm -rf 3rdparty ChangeLog.d docs pkgconfig .gitmodules .readthedocs.yaml
rm library/mps_*
cd ..
git add mbedtls

This time we leave library/psa_* present to enable TLS 1.3 features.

This is a complete overwrite of previous code so earlier changes in the
previous branch import/mbedtls-3.4.0 will be added on top of this commit.

Signed-off-by: Tom Van Eyck <tom.vaneyck@kuleuven.be>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/base64.c b/lib/libmbedtls/mbedtls/library/base64.c
index 4170610..9677dee 100644
--- a/lib/libmbedtls/mbedtls/library/base64.c
+++ b/lib/libmbedtls/mbedtls/library/base64.c
@@ -2,26 +2,17 @@
  *  RFC 1521 base64 encoding/decoding
  *
  *  Copyright The Mbed TLS Contributors
- *  SPDX-License-Identifier: Apache-2.0
- *
- *  Licensed under the Apache License, Version 2.0 (the "License"); you may
- *  not use this file except in compliance with the License.
- *  You may obtain a copy of the License at
- *
- *  http://www.apache.org/licenses/LICENSE-2.0
- *
- *  Unless required by applicable law or agreed to in writing, software
- *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *  See the License for the specific language governing permissions and
- *  limitations under the License.
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
  */
 
+#include <limits.h>
+
 #include "common.h"
 
 #if defined(MBEDTLS_BASE64_C)
 
 #include "mbedtls/base64.h"
+#include "base64_internal.h"
 #include "constant_time_internal.h"
 
 #include <stdint.h>
@@ -31,7 +22,38 @@
 #include "mbedtls/platform.h"
 #endif /* MBEDTLS_SELF_TEST */
 
-#define BASE64_SIZE_T_MAX   ((size_t) -1)   /* SIZE_T_MAX is not standard */
+MBEDTLS_STATIC_TESTABLE
+unsigned char mbedtls_ct_base64_enc_char(unsigned char value)
+{
+    unsigned char digit = 0;
+    /* For each range of values, if value is in that range, mask digit with
+     * the corresponding value. Since value can only be in a single range,
+     * only at most one masking will change digit. */
+    digit |= mbedtls_ct_uchar_in_range_if(0, 25, value, 'A' + value);
+    digit |= mbedtls_ct_uchar_in_range_if(26, 51, value, 'a' + value - 26);
+    digit |= mbedtls_ct_uchar_in_range_if(52, 61, value, '0' + value - 52);
+    digit |= mbedtls_ct_uchar_in_range_if(62, 62, value, '+');
+    digit |= mbedtls_ct_uchar_in_range_if(63, 63, value, '/');
+    return digit;
+}
+
+MBEDTLS_STATIC_TESTABLE
+signed char mbedtls_ct_base64_dec_value(unsigned char c)
+{
+    unsigned char val = 0;
+    /* For each range of digits, if c is in that range, mask val with
+     * the corresponding value. Since c can only be in a single range,
+     * only at most one masking will change val. Set val to one plus
+     * the desired value so that it stays 0 if c is in none of the ranges. */
+    val |= mbedtls_ct_uchar_in_range_if('A', 'Z', c, c - 'A' +  0 + 1);
+    val |= mbedtls_ct_uchar_in_range_if('a', 'z', c, c - 'a' + 26 + 1);
+    val |= mbedtls_ct_uchar_in_range_if('0', '9', c, c - '0' + 52 + 1);
+    val |= mbedtls_ct_uchar_in_range_if('+', '+', c, c - '+' + 62 + 1);
+    val |= mbedtls_ct_uchar_in_range_if('/', '/', c, c - '/' + 63 + 1);
+    /* At this point, val is 0 if c is an invalid digit and v+1 if c is
+     * a digit with the value v. */
+    return val - 1;
+}
 
 /*
  * Encode a buffer into base64 format
@@ -50,8 +72,8 @@
 
     n = slen / 3 + (slen % 3 != 0);
 
-    if (n > (BASE64_SIZE_T_MAX - 1) / 4) {
-        *olen = BASE64_SIZE_T_MAX;
+    if (n > (SIZE_MAX - 1) / 4) {
+        *olen = SIZE_MAX;
         return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
     }
 
@@ -94,7 +116,7 @@
         *p++ = '=';
     }
 
-    *olen = p - dst;
+    *olen = (size_t) (p - dst);
     *p = 0;
 
     return 0;
@@ -203,7 +225,7 @@
         }
     }
 
-    *olen = p - dst;
+    *olen = (size_t) (p - dst);
 
     return 0;
 }