Hello, according to RFC 4492 the key usage for ECDHE and ECDH ciphers need to be observed in regards to key agreement: When I use ECDH_ECDSA ciphers then the server certificate must have the keyAgreement usage. When I use ECDHE_ECDSA ciphers then the server certificate must have "digitalSignature".
# Note that there is no structural difference between ECDH and ECDSA # keys. A certificate issuer may use X.509 v3 keyUsage and # extendedKeyUsage extensions to restrict the use of an ECC public key # to certain computations [15 <https://tools.ietf.org/search/rfc4492#ref-15>]. This document refers to an ECC key as # ECDH-capable if its use in ECDH is permitted. ECDSA-capable is # defined similarly. This rule is enforced by the openssl s_client: when the server proposes a cipher which does not pass this check it will terminate the connection: > openssl s_client -cipher ECDHE-ECDSA-AES128-SHA256 -connect localhost:1234 > 1252:error:1411713E:SSL routines:ssl_check_srvr_ecc_cert_and_alg:ecc cert not for signing:.\ssl\ssl_lib.c:2512: > 1252:error:14082130:SSL routines:ssl3_check_cert_and_algorithm:bad ecc cert:.\ssl\s3_clnt.c:3544: In this case the certificate had key usage: > [ server-exch ] > extendedKeyUsage = serverAuth > basicConstraints = CA:FALSE > keyUsage = keyAgreement > subjectAltName=IP:127.0.0.1,DNS:localhost. The connect with static ECDH works: > openssl s_client -cipher ECDH-ECDSA-AES128-SHA256 -connect localhost:1234 ... > SSL-Session: > Protocol : TLSv1.2 > Cipher : ECDH-ECDSA-AES128-SHA256 The other way around, when I use the following key usage: > [ server-sign ] > extendedKeyUsage = serverAuth > basicConstraints = CA:FALSE > keyUsage = digitalSignature > subjectAltName=IP:127.0.0.1,DNS:localhost. OpenSSL client works this way: >openssl s_client -cipher ECDH-ECDSA-AES128-SHA256 -connect localhost:1234 >9916:error:1411713D:SSL routines:ssl_check_srvr_ecc_cert_and_alg:ecc cert not for key agreement >openssl s_client -cipher ECDHE-ECDSA-AES128-SHA256 -connect localhost:1234 >SSL-Session: > Protocol : TLSv1.2 > Cipher : ECDHE-ECDSA-AES128-SHA256 In both cases however JSSE (OracleJDK8u121 or OpenJDK 9-ea+162) will offer both cipher suites and not filter them by key usage capabilties. Would you agree this is a bug? And should this also apply to client side? I have not tested it with RSA certificates, but I would expect this to be the same. Gruss Bernd PS: config file and openssl commands to create multiple ECC certificates used for this test: https://gist.github.com/ecki/d66d79bf0cf12872d015804f5edec6e4
