Explanation of openssl ciphersuites I'm looking for a detailed explanation of the ciphersuites available in openssl.

openssl already offers the ciphers command which can be used to output, for example, the following:

$ openssl ciphers -v "HIGH,-SHA,-AES256"
DH-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(128) Mac=AEAD
DH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-SHA256   TLSv1.2 Kx=DH       Au=RSA  Enc=AES(128)  Mac=SHA256
DHE-DSS-AES128-SHA256   TLSv1.2 Kx=DH       Au=DSS  Enc=AES(128)  Mac=SHA256
DH-RSA-AES128-SHA256    TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AES(128)  Mac=SHA256
DH-DSS-AES128-SHA256    TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AES(128)  Mac=SHA256
ADH-AES128-GCM-SHA256   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(128) Mac=AEAD
ADH-AES128-SHA256       TLSv1.2 Kx=DH       Au=None Enc=AES(128)  Mac=SHA256
AES128-GCM-SHA256       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(128) Mac=AEAD
AES128-SHA256           TLSv1.2 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA256


It seems that ADH stands for "Anonymous Diffie-Hellman" but also implies specific groups and bit sizes.

I am interested in detailed explanations of what all the abbreviations are and generally which of these ciphersuites are considered secure.

Specifically:


What is ADH? Where is it standardized?
The listed MAC algorithms are hash functions. Is it using HMAC?
What does "Au" mean?
What is ADH? Where is it standardized?


ADH stands for Anonymous Diffie-Hellman, ie unauthenticated Diffie-Hellman, also called "opportunistic encryption". It has been part of the SSL/TLS standards at least since SSLv3. It was also extended to ECDHE in RFC4492.


  The listed MAC algorithms are hash functions. Is it using HMAC?


Yes indeed.


  What does "Au" mean?


It most likely means something like Authentication mechanism. This clearly covers with the given ciphersuites as ADH suites have none there, RSA key-transport and DHE+RSA suites have RSA there (server authenticated via RSA signature), DHE+DSS suites have DSS there (server authenticated via DSA) and suites using static DH ones have DH there (server authenticated via his static DH public key).