Add PQC introduction and why is important for Arm; Add scheme description.

Author: odincodeshen

content/learning-paths/embedded-and-microcontrollers/Introduction-to-pqm4-and-Post-Quantum-Cryptography/introduction.md

@@ -6,7 +6,32 @@ weight: 2
 layout: learningpathall
 ---
 
-The [pqm4](https://github.com/mupq/pqm4) library is a collection of post-quantum cryptographic algorithms designed for the ARM Cortex-M4 microcontrollers. It originated from the [PQCRYPTO](https://pqcrypto.eu.org) project, funded by the European Commission. The library includes implementations of post-quantum key-encapsulation mechanisms and signature schemes.
+### Post-Quantum Cryptography
+
+The [pqm4](https://github.com/mupq/pqm4) framework is a benchmarking and implementation suite for post-quantum cryptography (PQC) on Arm Cortex-M4 microcontrollers.  It originated from the [PQCRYPTO](https://pqcrypto.eu.org) project, funded by the European Commission, and has since evolved into a widely used platform for evaluating PQC in embedded environments.
+
+As quantum computing advances, widely used cryptographic schemes such as RSA and elliptic curve cryptography are expected to become insecure. This presents a unique challenge for embedded systems, where devices often remain deployed for 10 to 20 years and must be designed with long-term security in mind.
+
+Post-quantum cryptography is expected to play a critical role in securing a wide range of embedded applications, including secure firmware updates, device authentication, encrypted communication (e.g., IoT sensor-to-cloud), and integrity protection for edge AI models. These use cases require cryptographic mechanisms that remain secure over the lifetime of the device, even in the presence of future quantum adversaries.
+
+To address this, new PQC algorithms have been standardized by NIST, including ML-KEM for key exchange and ML-DSA for digital signatures. However, these algorithms are significantly more demanding in terms of computation, memory, and code size compared to classical cryptography — making their deployment on constrained microcontrollers non-trivial.
+
+The pqm4 framework provides a practical solution by enabling developers to evaluate PQC implementations under real embedded constraints. It offers standardized benchmarking for performance (cycle counts), memory usage (stack), and code size, along with optimized implementations tailored for the Cortex-M4 architecture. This allows developers to move beyond theoretical analysis and make informed decisions about deploying PQC in real-world embedded systems.
+
+
+### Two Public-key Primitives
+
+Two public-key primitives are particularly fundamental to modern cryptography: 
+- key encapsulation mechanisms (KEMs) and 
+- digital signature algorithms (DSAs). 
+
+KEMs allow two parties to establish a shared secret over an insecure channel - the foundation for encrypted communications in protocols like TLS. Digital signatures provide authentication and integrity, ensuring that a message genuinely comes from its claimed sender and hasn't been tampered with. Together, these primitives underpin everything from secure web browsing to firmware updates on embedded devices.
+
+Post-quantum cryptography replaces classical algorithms with new designs built on mathematical problems that remain hard even for quantum computers. Among the various primitives, KEMs and signatures are the most critical for most applications and have been the focus of NIST's standardization effort. KEMs have received particular urgency due to "harvest now, decrypt later" attacks - adversaries can record encrypted communications today and decrypt them once quantum computers become available.
+
+This makes protecting data in transit an immediate priority, even though quantum computers may still be years away. Unlike classical public-key cryptography, which relies almost entirely on integer factorization and discrete logarithms, PQC draws on a variety of foundations: Lattices, hash functions, error-correcting codes, multivariate polynomials, and more. This diversity means that different PQC schemes come with very different performance characteristics and trade-offs.
+
+In this learning path, we will focus on KEMs implementation on Cortex-M. 
 
 ### Benefits of pqm4 for ARM Developers
 

content/learning-paths/embedded-and-microcontrollers/Introduction-to-pqm4-and-Post-Quantum-Cryptography/running-tests-and-benchmarks.md

@@ -253,6 +253,15 @@ speed:  66%|██████████████████████
 speed: 100%|██████████████████████████████| 3/3 [01:00<00:00, 20.00s/it, ml-kem-768 - clean]
 ```
 
+For most of the schemes there are multiple implementations. 
+The naming scheme for these implementations is as follows:
+
+- clean: clean reference implementation from PQClean,
+- ref: the reference implementation submitted to NIST (will be replaced by clean in the long term),
+- opt: an optimized implementation in plain C (e.g., the optimized implementation submitted to NIST),
+- m4: an implementation with Cortex-M4 specific optimizations (typically in assembly).
+- m4f: an implementation with Cortex-M4F specific optimizations (typically assembly using floating-point registers).
+
 Expected output of the benchmark results is stored in the **benchmarks.csv** file
 
 ![benchmarks.csv](./benchmarks.png)