diff --git a/library/base64.c b/library/base64.c
index 3eb9e7c..3f13fda 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -33,6 +33,39 @@
 #include "mbedtls/platform.h"
 #endif /* MBEDTLS_SELF_TEST */
 
+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_mask_of_range(0, 25, value) & ('A' + value);
+    digit |= mbedtls_ct_uchar_mask_of_range(26, 51, value) & ('a' + value - 26);
+    digit |= mbedtls_ct_uchar_mask_of_range(52, 61, value) & ('0' + value - 52);
+    digit |= mbedtls_ct_uchar_mask_of_range(62, 62, value) & '+';
+    digit |= mbedtls_ct_uchar_mask_of_range(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_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;
+}
+
 /*
  * Encode a buffer into base64 format
  */