Mbed TLS (previously PolarSSL) is an implementation of the TLS and SSL protocols and the respective cryptographic algorithms and support code required. It is distributed under the

Apache License The Apache License is a permissive free software license written by the Apache Software Foundation (ASF). It allows users to use the software for any purpose, to distribute it, to modify it, and to distribute modified versions of the software ...

version 2.0. Stated on the website is that Mbed TLS aims to be "easy to understand, use, integrate and expand".

History

The PolarSSL SSL library is the official continuation fork of the XySSL SSL library. XySSL was created by the French "

white hat hacker A white hat (or a white-hat hacker, a whitehat) is an ethical security hacker. Ethical hacking is a term meant to imply a broader category than just penetration testing. Under the owner's consent, white-hat hackers aim to identify any vulnerabilit ...

" Christophe Devine and was first released on November 1, 2006, under

GNU GPL The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

v2 and

BSD The Berkeley Software Distribution (BSD), also known as Berkeley Unix or BSD Unix, is a discontinued Unix operating system developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley, beginni ...

licenses. In 2008, Christophe Devine was no longer able to support XySSL and allowed Paul Bakker to create the official fork, named PolarSSL. In November 2014, PolarSSL was acquired by

ARM Holdings Arm Holdings plc (formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a British semiconductor and software design company based in Cambridge, England, whose primary business is the design of central processing ...

. In 2011, the Dutch government approved an integration between

OpenVPN OpenVPN is a virtual private network (VPN) system that implements techniques to create secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It implements both client and server appl ...

and PolarSSL, which is named OpenVPN-NL. This version of OpenVPN has been approved for use in protecting government communications up to the level of Restricted. As of the release of version 1.3.10, PolarSSL has been rebranded to Mbed TLS to better show its fit inside the Mbed ecosystem. Starting from version 2.1.0, the library was made available under both the GPL v2 and Apache License v2.0. In 2020, Mbed TLS joined the TrustedFirmware project.

Library

The core SSL

library A library is a collection of Book, books, and possibly other Document, materials and Media (communication), media, that is accessible for use by its members and members of allied institutions. Libraries provide physical (hard copies) or electron ...

is written in the

C programming language C (''pronounced'' '' – like the letter c'') is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of ...

and implements the SSL module, the basic

cryptographic Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More gen ...

functions and provides various utility functions. Unlike

OpenSSL OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping, and identify the party at the other end. It is widely used by Internet servers, including the majority of HTTPS web ...

and other implementations of TLS, Mbed TLS is like wolfSSL in that it is designed to fit on small embedded devices, with the minimum complete TLS stack requiring under 60KB of program space and under 64 KB of RAM. It is also highly modular: each component, such as a cryptographic function, can be used independently from the rest of the framework. Versions are also available for

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

and

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

. Because Mbed TLS is written in the

, without external dependencies, it works on most operating systems and architectures. Since version 1.3.0, it has abstraction layers for memory allocation and threading to the core "to support better integration with existing embedded operating systems".

Design priorities

The Mbed TLS library expresses a focus on readability of the code, documentation, automated regression tests, a loosely coupled design and portable code.

Development documentation

The following documentation is available for developers: * High Level Design: a high level description of the different modules inside the library, with UML diagrams, use cases and interactions in common scenarios. * API documentation:

Doxygen Doxygen ( ) is a documentation generator that works with many programming languages. It extracts information from specially-formatted source code comments and saves the information in one of various supported formats. Doxygen supports static ...

-generated documentation from the header files of the library. * Source code documentation: The source code of the library is documented to clarify structures, decisions and code constructs.

Automated testing

The automated testing of Mbed TLS includes: * A test framework is included with the source code that contains over 5000 automated tests (based on the number of tests in version 1.3.2 of the library) to test for regressions and compatibility on different platforms. * A compatibility script (compat.sh) that tests compatibility of SSL communication with

and GnuTLS. * A

continuous integration Continuous integration (CI) is the practice of integrating source code changes frequently and ensuring that the integrated codebase is in a workable state. Typically, developers Merge (version control), merge changes to an Branching (revisio ...

system based on Travis CI and Jenkins.

Use

Mbed TLS is used as the SSL component in large open source projects: *

and OpenVPN-NL *

Hiawatha Hiawatha ( , also : ), also known as Ayenwatha or Aiionwatha, was a precolonial Native American leader and cofounder of the Iroquois Confederacy. He was a leader of the Onondaga people, the Mohawk people, or both. According to some accounts, he ...

PowerDNS PowerDNS is a Name server, DNS server program, written in C++ and licensed under the GNU General Public License, GPL. It runs on most Unix derivatives. PowerDNS features a large number of different ''backends'' ranging from simple BIND style z ...

* Monkey HTTP Server *

OpenWRT OpenWrt (from ''open wireless router'') is an open-source project for embedded operating systems based on Linux kernel, Linux, primarily used on Embedded system, embedded devices to Router (computing), route network traffic. The main components ...

Platforms

Mbed TLS is currently available for most Operating Systems including

OS X macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

OpenWrt OpenWrt (from ''open wireless router'') is an open-source project for embedded operating systems based on Linux kernel, Linux, primarily used on Embedded system, embedded devices to Router (computing), route network traffic. The main components ...

, Android,

iOS Ios, Io or Nio (, ; ; locally Nios, Νιός) is a Greek island in the Cyclades group in the Aegean Sea. Ios is a hilly island with cliffs down to the sea on most sides. It is situated halfway between Naxos and Santorini. It is about long an ...

RISC OS RISC OS () is an operating system designed to run on ARM architecture, ARM computers. Originally designed in 1987 by Acorn Computers of England, it was made for use in its new line of ARM-based Acorn Archimedes, Archimedes personal computers an ...

and

FreeRTOS FreeRTOS is a real-time operating system Kernel (operating system), kernel for embedded devices that has been ported to 40 microcontroller platforms. It is distributed under the MIT License. History The FreeRTOS kernel was originally developed ...

. Chipsets supported at least include ARM, x86, PowerPC, MIPS.

Algorithms

Mbed TLS supports a number of different cryptographic algorithms: ;

Cryptographic hash function A cryptographic hash function (CHF) is a hash algorithm (a map (mathematics), map of an arbitrary binary string to a binary string with a fixed size of n bits) that has special properties desirable for a cryptography, cryptographic application: ...

s: : MD2,

MD4 The MD4 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1990. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA-1 and RIPEMD algorithms. The initialism "MD" st ...

MD5 The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, and was specified in 1992 as Request for Comments, RFC 1321. MD5 ...

, RIPEMD160,

SHA-1 In cryptography, SHA-1 (Secure Hash Algorithm 1) is a hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest – typically rendered as 40 hexadecimal digits. It was designed by the United States ...

SHA-2 SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. They are built using the Merkle–Damgård construction, from a one-way compression ...

SHA-3 SHA-3 (Secure Hash Algorithm 3) is the latest member of the Secure Hash Algorithm family of standards, released by NIST on August 5, 2015. Although part of the same series of standards, SHA-3 is internally different from the MD5-like stru ...

;

MAC Mac or MAC may refer to: Common meanings * Mac (computer), a line of personal computers made by Apple Inc. * Mackintosh, a raincoat made of rubberized cloth * Mac, a prefix to surnames derived from Gaelic languages * McIntosh (apple), a Canadi ...

modes : CMAC,

HMAC In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a se ...

;

Cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

s: : AES,

ARIA In music, an aria (, ; : , ; ''arias'' in common usage; diminutive form: arietta, ; : ariette; in English simply air (music), air) is a self-contained piece for one voice, with or without instrument (music), instrumental or orchestral accompan ...

, Blowfish,

Camellia ''Camellia'' (pronounced or ) is a genus of flowering plants in the family Theaceae. They are found in tropical and subtropical areas in East Asia, eastern and South Asia, southern Asia, from the Himalayas east to Japan and Indonesia. There are ...

, ChaCha, DES, RC4,

Triple DES In cryptography, Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block. The 56-bit key of the Dat ...

, XTEA ; Cipher modes : ECB,

CBC CBC may refer to: Media * Cadena Baja California or Grupo Cadena, a radio and television broadcaster in Mexico * Canadian Broadcasting Corporation, Canada's radio and television public broadcaster ** CBC Television ** CBC Radio One ** CBC Music ** ...

, CFB, CTR, OFB, XTS ;

Authenticated encryption Authenticated Encryption (AE) is an encryption scheme which simultaneously assures the data confidentiality (also known as privacy: the encrypted message is impossible to understand without the knowledge of a secret key) and authenticity (in othe ...

modes : CCM, GCM,

NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...

Key Wrap, :

ChaCha20-Poly1305 ChaCha20-Poly1305 is an authenticated encryption with associated data (AEAD) algorithm, that combines the ChaCha20 stream cipher with the Poly1305 message authentication code. It has fast software performance, and without hardware acceleration, ...

; Key derivation : HKDF ;

Key stretching In cryptography, key stretching techniques are used to make a possibly weak key, typically a password or passphrase, more secure against a brute-force attack by increasing the resources (time and possibly space) it takes to test each possible ke ...

PBKDF2 In cryptography, PBKDF1 and PBKDF2 (Password-Based Key Derivation Function 1 and 2) are key derivation functions with a sliding computational cost, used to reduce vulnerability to brute-force attacks. PBKDF2 is part of RSA Laboratories' Public- ...

PKCS Public Key Cryptography Standards (PKCS) are a group of public-key cryptography standards devised and published by RSA Security LLC, starting in the early 1990s. The company published the standards to promote the use of the cryptography te ...

#5 PBE2, PKCS #12 key derivation ;

Public-key cryptography Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...

: : RSA,

Diffie–Hellman key exchange Diffie–Hellman (DH) key exchangeSynonyms of Diffie–Hellman key exchange include: * Diffie–Hellman–Merkle key exchange * Diffie–Hellman key agreement * Diffie–Hellman key establishment * Diffie–Hellman key negotiation * Exponential ke ...

, : Elliptic curve cryptography (ECC), Elliptic curve Diffie–Hellman (ECDH), Elliptic Curve DSA (ECDSA), Elliptic curve J-PAKE

References

External links

* {{DEFAULTSORT:Mbed TLS Cryptographic software C (programming language) libraries Free security software Transport Layer Security implementation 2009 software