From 3d4dba84b71ff669ac81e2f1520f0ef2ad486765 Mon Sep 17 00:00:00 2001
From: Gabor Mezei <gabor.mezei@arm.com>
Date: Mon, 15 Nov 2021 16:22:37 +0100
Subject: [PATCH] Move mbedtls_ct_base64_dec_value function to the
 constant-time module

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
---
 library/base64.c                 | 29 -----------------------------
 library/constant_time.c          | 28 ++++++++++++++++++++++++++++
 library/constant_time_internal.h |  2 ++
 3 files changed, 30 insertions(+), 29 deletions(-)

diff --git a/library/base64.c b/library/base64.c
index f1a605501..b2e6dabcb 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -109,35 +109,6 @@ int mbedtls_base64_encode( unsigned char *dst, size_t dlen, size_t *olen,
     return( 0 );
 }
 
-/* Given a Base64 digit, return its value.
- * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'),
- * return -1.
- *
- * The implementation assumes that letters are consecutive (e.g. ASCII
- * but not EBCDIC).
- *
- * The implementation is constant-flow (no branch or memory access depending
- * on the value of c) unless the compiler inlines and optimizes a specific
- * access.
- */
-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_mask_of_range( 'A', 'Z', c ) & ( c - 'A' +  0 + 1 );
-    val |= mbedtls_ct_uchar_mask_of_range( 'a', 'z', c ) & ( c - 'a' + 26 + 1 );
-    val |= mbedtls_ct_uchar_mask_of_range( '0', '9', c ) & ( c - '0' + 52 + 1 );
-    val |= mbedtls_ct_uchar_mask_of_range( '+', '+', c ) & ( c - '+' + 62 + 1 );
-    val |= mbedtls_ct_uchar_mask_of_range( '/', '/', 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 );
-}
-
 /*
  * Decode a base64-formatted buffer
  */
diff --git a/library/constant_time.c b/library/constant_time.c
index cdaa7fad9..5bf594fdd 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -344,6 +344,34 @@ unsigned char mbedtls_ct_base64_enc_char( unsigned char val )
     return( digit );
 }
 
+/* Given a Base64 digit, return its value.
+ * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'),
+ * return -1.
+ *
+ * The implementation assumes that letters are consecutive (e.g. ASCII
+ * but not EBCDIC).
+ *
+ * The implementation is constant-flow (no branch or memory access depending
+ * on the value of c) unless the compiler inlines and optimizes a specific
+ * access.
+ */
+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_mask_of_range( 'A', 'Z', c ) & ( c - 'A' +  0 + 1 );
+    val |= mbedtls_ct_uchar_mask_of_range( 'a', 'z', c ) & ( c - 'a' + 26 + 1 );
+    val |= mbedtls_ct_uchar_mask_of_range( '0', '9', c ) & ( c - '0' + 52 + 1 );
+    val |= mbedtls_ct_uchar_mask_of_range( '+', '+', c ) & ( c - '+' + 62 + 1 );
+    val |= mbedtls_ct_uchar_mask_of_range( '/', '/', 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 );
+}
+
 #endif /* MBEDTLS_BASE64_C */
 
 #if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
diff --git a/library/constant_time_internal.h b/library/constant_time_internal.h
index f0286221a..90d1ac673 100644
--- a/library/constant_time_internal.h
+++ b/library/constant_time_internal.h
@@ -171,6 +171,8 @@ void mbedtls_ct_mpi_uint_cond_assign( size_t n,
 
 unsigned char mbedtls_ct_base64_enc_char( unsigned char val );
 
+signed char mbedtls_ct_base64_dec_value( unsigned char c );
+
 #endif /* MBEDTLS_BASE64_C */
 
 #if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)