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Remove the support for CTR_DRBG. It's likely unused code, seeing as HMAC_DRBG is always enabled and prioritized over it unless NETLINK_CRYPTO is used to change the algorithm priorities. There's also no compelling reason to support more than one of [HMAC_DRBG, HASH_DRBG, CTR_DRBG]. By definition, callers cannot tell any difference in their outputs. And all are FIPS-certifiable, which is the only point of the kernel's NIST DRBGs anyway. Switching to CTR_DRBG doesn't seem all that compelling, either. While it's often the fastest NIST DRBG, it has several disadvantages: - CTR_DRBG uses AES. Some platforms don't have AES acceleration at all, causing a fallback to the table-based AES code which is very slow and can be vulnerable to cache-timing attacks. In contrast, HMAC_DRBG uses primitives that are consistently constant-time. - CTR_DRBG is usually considered to be somewhat less cryptographically robust than HMAC_DRBG. Granted, HMAC_DRBG isn't all that great either, e.g. given the negative result from Woodage & Shumow (2018) (https://eprint.iacr.org/2018/349.pdf), but that can be worked around. - CTR_DRBG is more complex than HMAC_DRBG, risking bugs. Indeed, while reviewing the CTR_DRBG code, I found two bugs, including one where it can return success while leaving the output buffer uninitialized. - The kernel's implementation of CTR_DRBG uses an "ctr(aes)" crypto_skcipher and relies on it returning the next counter value. That's fragile, and indeed historically many "ctr(aes)" crypto_skcipher implementations haven't done that. E.g. see commit511306b2d0("crypto: arm/aes-ce - update IV after partial final CTR block"), commitfa5fd3afc7("crypto: arm64/aes-blk - update IV after partial final CTR block"), commit371731ec21("crypto: atmel-aes - Fix saving of IV for CTR mode"), commit25baaf8e2c("crypto: crypto4xx - fix ctr-aes missing output IV"), commit334d37c9e2("crypto: caam - update IV using HW support"), commit0a4491d3fe("crypto: chelsio - count incomplete block in IV"), commite8e3c1ca57("crypto: s5p - update iv after AES-CBC op end"). I.e., there were many years where the kernel's CTR_DRBG code (if it were to have actually been used) repeated outputs on some platforms. AES-CTR also uses a 128-bit counter, which creates overflow edge cases that are sometimes gotten wrong. E.g. see commit009b30ac74("crypto: vmx - CTR: always increment IV as quadword"). So, while switching to CTR_DRBG for performance reasons isn't completely out of the question (notably BoringSSL uses it), it would take quite a bit more work to create a solid implementation of it in the kernel, including a more solid implementation of AES-CTR itself (in lib/crypto/, with a scalar bit-sliced fallback, etc). Since HMAC_DRBG has always been the default NIST DRBG variant in the kernel and is in a better state, let's just standardize on it for now. Signed-off-by: Eric Biggers <ebiggers@kernel.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. 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