CIPHERS.md: Explain Schannel error SEC_E_ALGORITHM_MISMATCH

If the SSL backend is Schannel and the user specifies an Schannel CALG_
that is not supported by the protocol or the server then curl returns
CURLE_SSL_CONNECT_ERROR (35) SEC_E_ALGORITHM_MISMATCH.

Fixes https://github.com/curl/curl/issues/3389
Closes https://github.com/curl/curl/pull/4106

diff --git a/docs/CIPHERS.md b/docs/CIPHERS.md
index 5b2dde18989e8560eee79a844971c14e0b674617..19aedf36fc30e47a4827219ad12050e07a5d58c1 100644 (file)
--- a/docs/CIPHERS.md
+++ b/docs/CIPHERS.md
@@ -461,6 +461,12 @@ specific ciphersuites. They are
 [defined](https://docs.microsoft.com/windows/desktop/SecCrypto/alg-id) by
 Microsoft.
 
+There is also the case that the selected algorithm is not supported by the
+protocol or does not match the ciphers offered by the server during the SSL
+negotiation. In this case curl will return error
+`CURLE_SSL_CONNECT_ERROR (35) SEC_E_ALGORITHM_MISMATCH`
+and the request will fail.
+
 `CALG_MD2`,
 `CALG_MD4`,
 `CALG_MD5`,