Merge tag 'mbedtls-2.16.1' into pr1813-2.16.0

Mbed TLS version 2.16.1

ChangeLog

 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS 2.x.x branch released xxxx-xx-xx
+= mbed TLS 2.16.1 branch released 2019-03-19
+
+Features
+   * Add MBEDTLS_REMOVE_3DES_CIPHERSUITES to allow removing 3DES ciphersuites
+     from the default list (enabled by default). See
+     https://sweet32.info/SWEET32_CCS16.pdf.
 
 Bugfix
    * Fix a compilation issue with mbedtls_ecp_restart_ctx not being defined
@@ -15,6 +20,43 @@ Bugfix
 Features
    * Add support for DTLS-SRTP as defined in RFC 5764. Based on #361 contributed
      by Johan Pascal.
+   * Fix clobber list in MIPS assembly for large integer multiplication.
+     Previously, this could lead to functionally incorrect assembly being
+     produced by some optimizing compilers, showing up as failures in
+     e.g. RSA or ECC signature operations. Reported in #1722, fix suggested
+     by Aurelien Jarno and submitted by Jeffrey Martin.
+   * Fix signed-to-unsigned integer conversion warning
+     in X.509 module. Fixes #2212.
+   * Reduce stack usage of `mpi_write_hlp()` by eliminating recursion.
+     Fixes #2190.
+   * Remove a duplicate #include in a sample program. Fixed by Masashi Honma #2326.
+   * Remove the mbedtls namespacing from the header file, to fix a "file not found"
+     build error. Fixed by Haijun Gu #2319.
+   * Fix returning the value 1 when mbedtls_ecdsa_genkey failed.
+   * Fix false failure in all.sh when backup files exist in include/mbedtls
+     (e.g. config.h.bak). Fixed by Peter Kolbus (Garmin) #2407.
+   * Ensure that unused bits are zero when writing ASN.1 bitstrings when using
+     mbedtls_asn1_write_bitstring().
+   * Fix issue when writing the named bitstrings in KeyUsage and NsCertType
+     extensions in CSRs and CRTs that caused these bitstrings to not be encoded
+     correctly as trailing zeroes were not accounted for as unused bits in the
+     leading content octet. Fixes #1610.
+
+Changes
+   * Include configuration file in all header files that use configuration,
+     instead of relying on other header files that they include.
+     Inserted as an enhancement for #1371
+   * Add support for alternative CSR headers, as used by Microsoft and defined
+     in RFC 7468. Found by Michael Ernst. Fixes #767.
+   * Fix configuration queries in ssl-opt.h. #2030
+   * Ensure that ssl-opt.h can be run in OS X. #2029
+   * Reduce the complexity of the timing tests. They were assuming more than the
+     underlying OS actually guarantees.
+   * Re-enable certain interoperability tests in ssl-opt.sh which had previously
+     been disabled for lack of a sufficiently recent version of GnuTLS on the CI.
+   * Ciphersuites based on 3DES now have the lowest priority by default when
+     they are enabled.
+>>>>>>> mbedtls-2.16.1
 
 = mbed TLS 2.16.0 branch released 2018-12-21
 

README.md

 README for Mbed TLS
 ===================
 
+Important
+---------
+
+This version of mbedtls is an aggregation of LTS mbedtls version together with pr1813 (for SRTP-DTLS support), a pull request
+maintained by Belledonne Communications SARL.
+
+
 Configuration
 -------------
 

doxygen/input/doc_mainpage.h

@@ -24,7 +24,7 @@
  */
 
 /**
- * @mainpage mbed TLS v2.16.0 source code documentation
+ * @mainpage mbed TLS v2.16.1 source code documentation
  *
  * This documentation describes the internal structure of mbed TLS.  It was
  * automatically generated from specially formatted comment blocks in

doxygen/mbedtls.doxyfile

@@ -28,7 +28,7 @@ DOXYFILE_ENCODING      = UTF-8
 # identify the project. Note that if you do not use Doxywizard you need
 # to put quotes around the project name if it contains spaces.
 
-PROJECT_NAME           = "mbed TLS v2.16.0"
+PROJECT_NAME           = "mbed TLS v2.16.1"
 
 # The PROJECT_NUMBER tag can be used to enter a project or revision number.
 # This could be handy for archiving the generated documentation or

include/mbedtls/aesni.h

@@ -27,6 +27,12 @@
 #ifndef MBEDTLS_AESNI_H
 #define MBEDTLS_AESNI_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "aes.h"
 
 #define MBEDTLS_AESNI_AES      0x02000000u

include/mbedtls/asn1write.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_ASN1_WRITE_H
 #define MBEDTLS_ASN1_WRITE_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "asn1.h"
 
 #define MBEDTLS_ASN1_CHK_ADD(g, f)                      \

include/mbedtls/base64.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_BASE64_H
 #define MBEDTLS_BASE64_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 #define MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL               -0x002A  /**< Output buffer too small. */

include/mbedtls/bn_mul.h

@@ -38,6 +38,12 @@
 #ifndef MBEDTLS_BN_MUL_H
 #define MBEDTLS_BN_MUL_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "bignum.h"
 
 #if defined(MBEDTLS_HAVE_ASM)
@@ -750,7 +756,7 @@
         "sw     $10, %2         \n\t"   \
         : "=m" (c), "=m" (d), "=m" (s)                      \
         : "m" (s), "m" (d), "m" (c), "m" (b)                \
-        : "$9", "$10", "$11", "$12", "$13", "$14", "$15"    \
+        : "$9", "$10", "$11", "$12", "$13", "$14", "$15", "lo", "hi" \
     );
 
 #endif /* MIPS */

include/mbedtls/ccm.h

@@ -49,6 +49,12 @@
 #ifndef MBEDTLS_CCM_H
 #define MBEDTLS_CCM_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "cipher.h"
 
 #define MBEDTLS_ERR_CCM_BAD_INPUT       -0x000D /**< Bad input parameters to the function. */

include/mbedtls/certs.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_CERTS_H
 #define MBEDTLS_CERTS_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 #ifdef __cplusplus

include/mbedtls/cipher.h

@@ -36,7 +36,7 @@
 #endif
 
 #include <stddef.h>
-#include "mbedtls/platform_util.h"
+#include "platform_util.h"
 
 #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
 #define MBEDTLS_CIPHER_MODE_AEAD

include/mbedtls/cmac.h

@@ -28,6 +28,12 @@
 #ifndef MBEDTLS_CMAC_H
 #define MBEDTLS_CMAC_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "cipher.h"
 
 #ifdef __cplusplus

include/mbedtls/compat-1.3.h

@@ -25,6 +25,12 @@
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #if ! defined(MBEDTLS_DEPRECATED_REMOVED)
 
 #if defined(MBEDTLS_DEPRECATED_WARNING)

include/mbedtls/config.h

@@ -686,6 +686,26 @@
  */
 #define MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 
+/**
+ * \def MBEDTLS_REMOVE_3DES_CIPHERSUITES
+ *
+ * Remove 3DES ciphersuites by default in SSL / TLS.
+ * This flag removes the ciphersuites based on 3DES from the default list as
+ * returned by mbedtls_ssl_list_ciphersuites(). However, it is still possible
+ * to enable (some of) them with mbedtls_ssl_conf_ciphersuites() by including
+ * them explicitly.
+ *
+ * A man-in-the-browser attacker can recover authentication tokens sent through
+ * a TLS connection using a 3DES based cipher suite (see "On the Practical
+ * (In-)Security of 64-bit Block Ciphers" by Karthikeyan Bhargavan and Gaëtan
+ * Leurent, see https://sweet32.info/SWEET32_CCS16.pdf). If this attack falls
+ * in your threat model or you are unsure, then you should keep this option
+ * enabled to remove 3DES based cipher suites.
+ *
+ * Comment this macro to keep 3DES in the default ciphersuite list.
+ */
+#define MBEDTLS_REMOVE_3DES_CIPHERSUITES
+
 /**
  * \def MBEDTLS_ECP_DP_SECP192R1_ENABLED
  *

include/mbedtls/ctr_drbg.h

@@ -36,6 +36,12 @@
 #ifndef MBEDTLS_CTR_DRBG_H
 #define MBEDTLS_CTR_DRBG_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "aes.h"
 
 #if defined(MBEDTLS_THREADING_C)

include/mbedtls/ecdh.h

@@ -34,6 +34,12 @@
 #ifndef MBEDTLS_ECDH_H
 #define MBEDTLS_ECDH_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ecp.h"
 
 /*

include/mbedtls/ecdsa.h

@@ -32,6 +32,12 @@
 #ifndef MBEDTLS_ECDSA_H
 #define MBEDTLS_ECDSA_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ecp.h"
 #include "md.h"
 

include/mbedtls/ecjpake.h

@@ -40,6 +40,11 @@
  * The payloads are serialized in a way suitable for use in TLS, but could
  * also be use outside TLS.
  */
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
 
 #include "ecp.h"
 #include "md.h"

include/mbedtls/ecp.h

@@ -36,6 +36,12 @@
 #ifndef MBEDTLS_ECP_H
 #define MBEDTLS_ECP_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "bignum.h"
 
 /*

include/mbedtls/ecp_internal.h

@@ -61,6 +61,12 @@
 #ifndef MBEDTLS_ECP_INTERNAL_H
 #define MBEDTLS_ECP_INTERNAL_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #if defined(MBEDTLS_ECP_INTERNAL_ALT)
 
 /**

include/mbedtls/error.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_ERROR_H
 #define MBEDTLS_ERROR_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 /**

include/mbedtls/gcm.h

@@ -33,6 +33,12 @@
 #ifndef MBEDTLS_GCM_H
 #define MBEDTLS_GCM_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "cipher.h"
 
 #include <stdint.h>

include/mbedtls/havege.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_HAVEGE_H
 #define MBEDTLS_HAVEGE_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 #define MBEDTLS_HAVEGE_COLLECT_SIZE 1024

include/mbedtls/hkdf.h

@@ -27,6 +27,12 @@
 #ifndef MBEDTLS_HKDF_H
 #define MBEDTLS_HKDF_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "md.h"
 
 /**

include/mbedtls/hmac_drbg.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_HMAC_DRBG_H
 #define MBEDTLS_HMAC_DRBG_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "md.h"
 
 #if defined(MBEDTLS_THREADING_C)

include/mbedtls/net.h

@@ -23,6 +23,11 @@
  *
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
 
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
 #include "net_sockets.h"

include/mbedtls/nist_kw.h

@@ -37,6 +37,12 @@
 #ifndef MBEDTLS_NIST_KW_H
 #define MBEDTLS_NIST_KW_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "cipher.h"
 
 #ifdef __cplusplus

include/mbedtls/padlock.h

@@ -28,6 +28,12 @@
 #ifndef MBEDTLS_PADLOCK_H
 #define MBEDTLS_PADLOCK_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "aes.h"
 
 #define MBEDTLS_ERR_PADLOCK_DATA_MISALIGNED               -0x0030  /**< Input data should be aligned. */

include/mbedtls/pem.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_PEM_H
 #define MBEDTLS_PEM_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 /**

include/mbedtls/pkcs12.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_PKCS12_H
 #define MBEDTLS_PKCS12_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "md.h"
 #include "cipher.h"
 #include "asn1.h"

include/mbedtls/pkcs5.h

@@ -26,6 +26,12 @@
 #ifndef MBEDTLS_PKCS5_H
 #define MBEDTLS_PKCS5_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "asn1.h"
 #include "md.h"
 

include/mbedtls/platform_util.h

@@ -26,14 +26,14 @@
 #define MBEDTLS_PLATFORM_UTIL_H
 
 #if !defined(MBEDTLS_CONFIG_FILE)
-#include "mbedtls/config.h"
+#include "config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif
 
 #include <stddef.h>
 #if defined(MBEDTLS_HAVE_TIME_DATE)
-#include "mbedtls/platform_time.h"
+#include "platform_time.h"
 #include <time.h>
 #endif /* MBEDTLS_HAVE_TIME_DATE */
 

include/mbedtls/poly1305.h

@@ -34,7 +34,7 @@
 #define MBEDTLS_POLY1305_H
 
 #if !defined(MBEDTLS_CONFIG_FILE)
-#include "mbedtls/config.h"
+#include "config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif

include/mbedtls/ssl_cache.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_CACHE_H
 #define MBEDTLS_SSL_CACHE_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ssl.h"
 
 #if defined(MBEDTLS_THREADING_C)

include/mbedtls/ssl_ciphersuites.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_CIPHERSUITES_H
 #define MBEDTLS_SSL_CIPHERSUITES_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "pk.h"
 #include "cipher.h"
 #include "md.h"

include/mbedtls/ssl_cookie.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_COOKIE_H
 #define MBEDTLS_SSL_COOKIE_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ssl.h"
 
 #if defined(MBEDTLS_THREADING_C)

include/mbedtls/ssl_internal.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_INTERNAL_H
 #define MBEDTLS_SSL_INTERNAL_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ssl.h"
 #include "cipher.h"
 

include/mbedtls/ssl_ticket.h

@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_TICKET_H
 #define MBEDTLS_SSL_TICKET_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 /*
  * This implementation of the session ticket callbacks includes key
  * management, rotating the keys periodically in order to preserve forward

include/mbedtls/version.h

@@ -40,16 +40,16 @@
  */
 #define MBEDTLS_VERSION_MAJOR  2
 #define MBEDTLS_VERSION_MINOR  16
-#define MBEDTLS_VERSION_PATCH  0
+#define MBEDTLS_VERSION_PATCH  1
 
 /**
  * The single version number has the following structure:
  *    MMNNPP00
  *    Major version | Minor version | Patch version
  */
-#define MBEDTLS_VERSION_NUMBER         0x02100000
-#define MBEDTLS_VERSION_STRING         "2.16.0"
-#define MBEDTLS_VERSION_STRING_FULL    "mbed TLS 2.16.0"
+#define MBEDTLS_VERSION_NUMBER         0x02100100
+#define MBEDTLS_VERSION_STRING         "2.16.1"
+#define MBEDTLS_VERSION_STRING_FULL    "mbed TLS 2.16.1"
 
 #if defined(MBEDTLS_VERSION_C)
 

include/mbedtls/x509_csr.h

@@ -205,6 +205,14 @@ void mbedtls_x509write_csr_set_md_alg( mbedtls_x509write_csr *ctx, mbedtls_md_ty
  * \param key_usage key usage flags to set
  *
  * \return          0 if successful, or MBEDTLS_ERR_X509_ALLOC_FAILED
+ *
+ * \note            The <code>decipherOnly</code> flag from the Key Usage
+ *                  extension is represented by bit 8 (i.e.
+ *                  <code>0x8000</code>), which cannot typically be represented
+ *                  in an unsigned char. Therefore, the flag
+ *                  <code>decipherOnly</code> (i.e.
+ *                  #MBEDTLS_X509_KU_DECIPHER_ONLY) cannot be set using this
+ *                  function.
  */
 int mbedtls_x509write_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage );
 

library/CMakeLists.txt

@@ -98,6 +98,12 @@ if(CMAKE_COMPILER_IS_CLANG)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wmissing-declarations -Wmissing-prototypes -Wdocumentation -Wno-documentation-deprecated-sync -Wunreachable-code")
 endif(CMAKE_COMPILER_IS_CLANG)
 
+if(UNSAFE_BUILD)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-error")
+    set(CMAKE_C_FLAGS_ASAN "${CMAKE_C_FLAGS_ASAN} -Wno-error")
+    set(CMAKE_C_FLAGS_ASANDBG "${CMAKE_C_FLAGS_ASANDBG} -Wno-error")
+endif(UNSAFE_BUILD)
+
 if(WIN32)
     set(libs ${libs} ws2_32)
 endif(WIN32)
@@ -159,15 +165,15 @@ endif(USE_STATIC_MBEDTLS_LIBRARY)
 
 if(USE_SHARED_MBEDTLS_LIBRARY)
     add_library(mbedcrypto SHARED ${src_crypto})
-    set_target_properties(mbedcrypto PROPERTIES VERSION 2.16.0 SOVERSION 3)
+    set_target_properties(mbedcrypto PROPERTIES VERSION 2.16.1 SOVERSION 3)
     target_link_libraries(mbedcrypto ${libs})
 
     add_library(mbedx509 SHARED ${src_x509})
-    set_target_properties(mbedx509 PROPERTIES VERSION 2.16.0 SOVERSION 0)
+    set_target_properties(mbedx509 PROPERTIES VERSION 2.16.1 SOVERSION 0)
     target_link_libraries(mbedx509 ${libs} mbedcrypto)
 
     add_library(mbedtls SHARED ${src_tls})
-    set_target_properties(mbedtls PROPERTIES VERSION 2.16.0 SOVERSION 12)
+    set_target_properties(mbedtls PROPERTIES VERSION 2.16.1 SOVERSION 12)
     target_link_libraries(mbedtls ${libs} mbedx509)
 
     install(TARGETS mbedtls mbedx509 mbedcrypto

library/asn1write.c

@@ -294,22 +294,28 @@ int mbedtls_asn1_write_bitstring( unsigned char **p, unsigned char *start,
                           const unsigned char *buf, size_t bits )
 {
     int ret;
-    size_t len = 0, size;
+    size_t len = 0;
+    size_t unused_bits, byte_len;
 
-    size = ( bits / 8 ) + ( ( bits % 8 ) ? 1 : 0 );
+    byte_len = ( bits + 7 ) / 8;
+    unused_bits = ( byte_len * 8 ) - bits;
 
-    // Calculate byte length
-    //
-    if( *p < start || (size_t)( *p - start ) < size + 1 )
+    if( *p < start || (size_t)( *p - start ) < byte_len + 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
-    len = size + 1;
-    (*p) -= size;
-    memcpy( *p, buf, size );
+    len = byte_len + 1;
 
-    // Write unused bits
-    //
-    *--(*p) = (unsigned char) (size * 8 - bits);
+    /* Write the bitstring. Ensure the unused bits are zeroed */
+    if( byte_len > 0 )
+    {
+        byte_len--;
+        *--( *p ) = buf[byte_len] & ~( ( 0x1 << unused_bits ) - 1 );
+        ( *p ) -= byte_len;
+        memcpy( *p, buf, byte_len );
+    }
+
+    /* Write unused bits */
+    *--( *p ) = (unsigned char)unused_bits;
 
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BIT_STRING ) );

library/bignum.c

@@ -527,26 +527,38 @@ cleanup:
 }
 
 /*
- * Helper to write the digits high-order first
+ * Helper to write the digits high-order first.
  */
-static int mpi_write_hlp( mbedtls_mpi *X, int radix, char **p )
+static int mpi_write_hlp( mbedtls_mpi *X, int radix,
+                          char **p, const size_t buflen )
 {
     int ret;
     mbedtls_mpi_uint r;
+    size_t length = 0;
+    char *p_end = *p + buflen;
 
-    if( radix < 2 || radix > 16 )
-        return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+    do
+    {
+        if( length >= buflen )
+        {
+            return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+        }
 
-    MBEDTLS_MPI_CHK( mbedtls_mpi_mod_int( &r, X, radix ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_div_int( X, NULL, X, radix ) );
+        MBEDTLS_MPI_CHK( mbedtls_mpi_mod_int( &r, X, radix ) );
+        MBEDTLS_MPI_CHK( mbedtls_mpi_div_int( X, NULL, X, radix ) );
+        /*
+         * Write the residue in the current position, as an ASCII character.
+         */
+        if( r < 0xA )
+            *(--p_end) = (char)( '0' + r );
+        else
+            *(--p_end) = (char)( 'A' + ( r - 0xA ) );
 
-    if( mbedtls_mpi_cmp_int( X, 0 ) != 0 )
-        MBEDTLS_MPI_CHK( mpi_write_hlp( X, radix, p ) );
+        length++;
+    } while( mbedtls_mpi_cmp_int( X, 0 ) != 0 );
 
-    if( r < 10 )
-        *(*p)++ = (char)( r + 0x30 );
-    else