Update Intro and added details about BS signature

draft-ietf-pquip-pqc-engineers.md

@@ -220,7 +220,10 @@ The advent of a Cryptographically Relevant Quantum Computer (CRQC) would render
 
 Quantum computing is no longer perceived as a conjecture of computational sciences and theoretical physics. Considerable research efforts and enormous corporate and government funding for the development of practical quantum computing systems are being invested currently. At the time of writing the document, Cryptographically Relevant Quantum Computers (CRQCs) that can break widely used public-key cryptographic algorithms are not yet available. However, it is worth noting that there is ongoing research and development in the field of quantum computing, with the goal of building more powerful and scalable quantum computers. One common myth is that quantum computers are faster than conventional CPUs and GPUs in all areas. This is not the case; much as GPUs outperform general-purpose CPUs only on specific types of problems, so too will quantum computers have a niche set of problems on which they excel; unfortunately for cryptographers, integer factorization and discrete logarithms, the mathematical problems underpinning all of modern cryptography, happen to fall within the niche that we expect quantum computers to excel at. As such, as quantum technology advances, there is the potential for future quantum computers to have a significant impact on current cryptographic systems. Predicting the emergence of CRQC is a challenging task, and there is ongoing uncertainty regarding when they will become practically feasible.
 
-Extensive research has produced several "post-quantum cryptographic (PQC) algorithms" (sometimes referred to as "quantum-safe" algorithms) that offer the potential to ensure cryptography's survival in the quantum computing era. However, transitioning to a post-quantum infrastructure is not a straightforward task, and there are numerous challenges to overcome. It requires a combination of engineering efforts, proactive assessment and evaluation of available technologies, and a careful approach to product development. This document aims to provide general guidance to engineers who utilize public-key cryptography in their software. It covers topics such as selecting appropriate PQC algorithms, understanding the differences between PQC Key Encapsulation Mechanisms (KEMs) and traditional Diffie-Hellman and RSA style key exchange, and provides insights into expected key sizes and processing time differences between PQC algorithms and traditional ones. Additionally, it discusses the potential threat to symmetric cryptography from Cryptographically Relevant Quantum Computers (CRQCs).  It is important to remember that asymmetric algorithms (also known as public key algorithms) are largely used for secure communications between organizations or endpoints that may not have previously interacted, so a significant amount of coordination between organizations, and within and between ecosystems needs to be taken into account.  Such transitions are some of the most complicated in the tech industry and will require staged migrations in which upgraded agents need to co-exist and communicate with non-upgraded agents at a scale never before undertaken. It might be worth mentioning that recently National Security Agency (NSA) released an article on Future Quantum-Resistant (QR) Algorithm Requirements for National Security Systems {{CNSA2-0}} based on the need to protect against deployments of CRQCs in the future. German Federal Office for Information Security (BSI) has also released a PQC migration and recommendations document [BSI-PQC] which largely aligns with United States National Institute of Standards and Technology (NIST) and NSA guidance, but does differ on some of the guidance.
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+Extensive research has produced several "post-quantum cryptographic (PQC) algorithms" (sometimes referred to as "quantum-safe" algorithms) that offer the potential to ensure cryptography's survival in the quantum computing era. However, transitioning to a post-quantum infrastructure is not a straightforward task, and there are numerous challenges to overcome. It requires a combination of engineering efforts, proactive assessment and evaluation of available technologies, and a careful approach to product development. As the possibility of Cryptographically Relevant Quantum Computers (CRQCs) draws nearer, engineers responsible for designing, maintaining, and securing cryptographic systems must prepare for the significant changes that CRQCs will bring. Engineers need to understand how to implement post-quantum algorithms in applications, how to evaluate the trade-offs between security and performance, and how to ensure backward compatibility with current systems where needed. This is not merely a one-for-one replacement of algorithms; in many cases, the shift to PQC will involve redesigning protocols and infrastructure to accommodate the significant differences in resource utilization and key sizes between traditional and PQC algorithms.
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+This document aims to provide general guidance to engineers working on cryptographic libraries, network security, and infrastructure development, where long-term security planning is crucial. It covers topics such as selecting appropriate PQC algorithms, understanding the differences between PQC Key Encapsulation Mechanisms (KEMs) and traditional Diffie-Hellman and RSA style key exchange, and provides insights into expected key sizes and processing time differences between PQC algorithms and traditional ones. Additionally, it discusses the potential threat to symmetric cryptography from Cryptographically Relevant Quantum Computers (CRQCs).  It is important to remember that asymmetric algorithms (also known as public key algorithms) are largely used for secure communications between organizations or endpoints that may not have previously interacted, so a significant amount of coordination between organizations, and within and between ecosystems needs to be taken into account.  Such transitions are some of the most complicated in the tech industry and will require staged migrations in which upgraded agents need to co-exist and communicate with non-upgraded agents at a scale never before undertaken. It might be worth mentioning that recently National Security Agency (NSA) released an article on Future Quantum-Resistant (QR) Algorithm Requirements for National Security Systems {{CNSA2-0}} based on the need to protect against deployments of CRQCs in the future. German Federal Office for Information Security (BSI) has also released a PQC migration and recommendations document [BSI-PQC] which largely aligns with United States National Institute of Standards and Technology (NIST) and NSA guidance, but does differ on some of the guidance.
 
 It is important to note that CRQCs pose a threat to both symmetric and asymmetric cryptographic schemes. However, the threat to asymmetric cryptography is significantly greater due to Shor's algorithm, which can break widely-used public key schemes like RSA and ECC. Symmetric cryptography and hash functions also face some risk from Grover's algorithm, although the impact is less severe and can typically be mitigated by doubling key lengths. It is crucial for the reader to understand that when the word "PQC" is mentioned in the document, it means Asymmetric Cryptography (or Public key Cryptography) and not any algorithms from the Symmetric side based on stream, block ciphers, hash functions, MACs, etc, which are less vulnerable to quantum computers. This document does not cover such topics as when traditional algorithms might become vulnerable (for that, see documents such as [QC-DNS] and others).  It also does not cover unrelated technologies like Quantum Key Distribution or Quantum Key Generation, which use quantum hardware to exploit quantum effects to protect communications and generate keys, respectively.  Post-quantum cryptography is based on conventional (i.e., non-quantum) math and software and can be run on any general purpose computer.
 
@@ -272,6 +275,10 @@ Any asymmetric cryptographic algorithm based on integer factorization, finite fi
 
 * Digital Signatures: Digital Signature schemes are used to authenticate the identity of a sender, detect unauthorized modifications to data and underpin trust in a system. Similar to Key Agreement, signatures also depend on a public-private key pair based on the same mathematics as for Key Agreement and Key Transport, and hence a break in public key cryptography will also affect traditional digital signatures, hence the importance of developing post-quantum digital signatures.
 
+* BBS Signatures: BBS (Boneh-Boyen-Shacham) signatures are a privacy-preserving signature scheme that offers zero-knowledge proof-like properties by allowing selective disclosure of specific signed attributes without revealing the entire set of signed data. BBS signatures rely on the discrete logarithm problem, making them vulnerable to quantum attacks. A CRQC can break the data authenticity security property of BBS but not the data confidentiality (Section 6.9 of {{?I-D.irtf-cfrg-bbs-signatures}}).
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+* Content Encryption: Content encryption typically refers to the encryption of the data using symmetric key algorithms, such as AES, to ensure confidentiality. The threat to symmetric cryptography is discussed in {{symmetric}}.
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 # Invariants of Post-Quantum Cryptography: Necessitating Compliance Adjustments
 
 In the context of PQC, symmetric-key cryptographic algorithms are generally not directly impacted by quantum computing advancements. Symmetric-key cryptography, which includes keyed primitives such as block ciphers (e.g., AES) and message authentication mechanisms (e.g., HMAC-SHA2), rely on secret keys shared between the sender and receiver. Symmetric cryptography also includes hash functions (e.g., SHA-256) that are used for secure message digesting without any shared key material. HMAC is a specific construction that utilizes a cryptographic hash function (such as SHA-2) and a secret key shared between the sender and receiver to produce a message authentication code.