Bouncy Castle for .NET is a comprehensive, production-grade cryptographic library providing implementations of a vast range of symmetric and asymmetric ciphers, hash functions, message authentication codes, digital signatures, key agreement protocols, key encapsulation mechanisms (including post-quantum schemes like ML-KEM, ML-DSA, SLH-DSA), secure random number generation (NIST SP 800-90A DRBG), and ASN.1 encoding/decoding (DER, BER, DL). It supports high-level protocol implementations for TLS/DTLS (client and server, including PSK, SRP, and post-quantum key exchange), OpenPGP (RFC 4880/9580), CMS (Cryptographic Message Syntax), CMP, CRMF, OCSP, TSP, and X.509 certificate generation and validation. The library is designed as a class library with a monolithic architecture organized into namespaces (Org.BouncyCastle.Crypto, .Asn1, .Tls, .Bcpg, .Cms, etc.), exposing both low-level primitives and high-level builders. It targets multiple .NET runtimes with conditional compilation for hardware intrinsics (AES-NI, PCLMULQDQ, SSE/AVX) and Span<T> support. The codebase is actively maintained, with ongoing migration from older algorithm names (e.g., Dilithium → ML-DSA) and extensive use of factory patterns and interface-based abstractions, making it a solid foundation for secure application development.