document specs [skip ci] (open-quantum-safe#190)

* document specs [skip ci]

* Update README.md

Co-authored-by: Douglas Stebila <dstebila@users.noreply.github.com>

* complete reference to standards implemented [skip ci]

---------

Co-authored-by: Douglas Stebila <dstebila@users.noreply.github.com>
Signed-off-by: Felipe Ventura <felipe.ventura@entrust.com>

README.md

@@ -29,6 +29,36 @@ mechanism and X.509 data structures. Also available is support for
 TLS1.3 signature functionality via the [OpenSSL3 fetchable signature
 algorithm feature](https://github.com/openssl/openssl/pull/19312).
 
+Standards implemented
+---------------------
+
+For non-post-quantum algorithms, this provider is basically silent, i.e.,
+permits use of standards and algorithms implemented by [openssl](https://github.com/openssl/openssl)
+, e.g., concerning X.509, PKCS#8 or CMS.
+
+For post-quantum algorithms, the version of the cryptographic algorithm used
+depends on the version of [liboqs](https://github.com/open-quantum-safe/liboqs) used.
+Regarding the integration of post-quantum algorithms into higher level
+components, this provider implements the following standards:
+
+- For TLS:
+  - Hybrid post-quantum / traditional key exchange:
+    - The data structures used follow the Internet-Draft [Hybrid key exchange in TLS 1.3](https://datatracker.ietf.org/doc/draft-ietf-tls-hybrid-design/), namely simple concatenation of traditional and post-quantum public keys and shared secrets.
+    - The algorithm identifiers used are documented in [oqs-kem-info.md](https://github.com/open-quantum-safe/oqs-provider/blob/main/oqs-template/oqs-kem-info.md).
+  - Hybrid post-quantum / traditional signatures in TLS:
+    - For public keys and digital signatures inside X.509 certificates, see the bullet point on X.509 below.
+    - For digital signatures outside X.509 certificates and in the TLS 1.3 handshake directly, the data structures used follow the same encoding format as that used for X.509 certificates, namely simple concatenation of traditional and post-quantum signatures.
+    - The algorithm identifiers used are documented in [oqs-sig-info.md](https://github.com/open-quantum-safe/oqs-provider/blob/main/oqs-template/oqs-sig-info.md).
+- For X.509:
+  - Hybrid post-quantum / traditional public keys and signatures:
+    - The data structures used follow the Internet-Draft [Internet X.509 Public Key Infrastructure: Algorithm Identifiers for Dilithium](https://datatracker.ietf.org/doc/draft-ietf-lamps-dilithium-certificates/), namely simple concatenation of traditional and post-quantum components in plain binary / OCTET_STRING representations.
+    - The algorithm identifiers (OIDs) used are documented in [oqs-sig-info.md](https://github.com/open-quantum-safe/oqs-provider/blob/main/oqs-template/oqs-sig-info.md).
+- For PKCS#8:
+  - Hybrid post-quantum / traditional private keys:
+    - Simple concatenation of traditional and post-quantum components in plain binary / OCTET_STRING representations.
+
+Additionally worthwhile noting is that only quantum-safe [signature algorithms](#signature-algorithms) are persisted via PKCS#8 and X.509. No corresponding encoder/decoder logic exists for quantum safe [KEM algorithms](#kem-algorithms) -- See also #194.
+
 Algorithms
 ----------