OpenSSL 3.6 adds LMS signature verification & NIST security categories for PKEY objects

OpenSSL 3.6 has been released, introducing major security and compatibility changes for developers and administrators using this toolkit for TLS/SSL, Datagram Transport Layer Security (DTLS), and QUIC protocols. This update adds NIST security categories to PKEY objects, aligning key storage and handling with current standards. It also brings LMS signature verification based on [SP 800-208] to both the FIPS and default providers, expanding compliance options.

In addition, the release expands cryptographic API capabilities by supporting EVP_SKEY opaque symmetric key objects within key derivation and exchange provider methods. Several new functions have been added, including EVP_KDF_CTX_set_SKEY(), EVP_KDF_derive_SKEY(), and EVP_PKEY_derive_SKEY(). Building OpenSSL now requires compilers that support C-99 features, as the legacy ANSI-C toolchain is no longer sufficient.

While these enhancements broaden usage options, support for the VxWorks platform has been removed in this version. Administrators benefit from the new openssl configutl utility, which processes and outputs OpenSSL configuration files. Following these changes, FIPS provider users also gain support for deterministic ECDSA signature generation, as defined in FIPS 186-5. Finally, developers should note that EVP_PKEY_ASN1_METHOD-related functions have been deprecated, signaling further API modernization.