The following is a list of all permitted cipher strings and their meanings.
DEFAULT
the default cipher list. This is determined at compile time and, as of OpenSSL 1.0.0, is normally ALL:!aNULL:!eNULL. This must be the first cipher string specified.
COMPLEMENTOFDEFAULT
the ciphers included in ALL, but not enabled by default. Currently this is ADH. Note that this rule does not cover eNULL, which is not included by ALL (use COMPLEMENTOFALL if necessary).
ALL
all cipher suites except the eNULL ciphers which must be explicitly enabled; as of OpenSSL, the ALL cipher suites are reasonably ordered by default
COMPLEMENTOFALL
the cipher suites not enabled by ALL, currently being eNULL.
HIGH
"high" encryption cipher suites. This currently means those with key lengths larger than 128 bits, and some cipher suites with 128-bit keys.
MEDIUM
"medium" encryption cipher suites, currently some of those using 128 bit encryption.
LOW
"low" encryption cipher suites, currently those using 64 or 56 bit encryption algorithms but excluding export cipher suites.
EXP, EXPORT
export encryption algorithms. Including 40 and 56 bits algorithms.
EXPORT40
40 bit export encryption algorithms
EXPORT56
56 bit export encryption algorithms. In OpenSSL 0.9.8c and later the set of 56 bit export ciphers is empty unless OpenSSL has been explicitly configured with support for experimental ciphers.
eNULL, NULL
the "NULL" ciphers that is those offering no encryption. Because these offer no encryption at all and are a security risk they are disabled unless explicitly included.
aNULL
the cipher suites offering no authentication. This is currently the anonymous DH algorithms. These cipher suites are vulnerable to a "man in the middle" attack and so their use is normally discouraged.
kRSA, RSA
cipher suites using RSA key exchange.
kEDH
cipher suites using ephemeral DH key agreement.
kDHr, kDHd
cipher suites using DH key agreement and DH certificates signed by CAs with RSA and DSS keys respectively. Not implemented.
aRSA
cipher suites using RSA authentication, i.e. the certificates carry RSA keys.
aDSS, DSS
cipher suites using DSS authentication, i.e. the certificates carry DSS keys.
aDH
cipher suites effectively using DH authentication, i.e. the certificates carry DH keys. Not implemented.
kFZA, aFZA, eFZA, FZA
ciphers suites using FORTEZZA key exchange, authentication, encryption or all FORTEZZA algorithms. Not implemented.
TLSv1, SSLv3, SSLv2
TLS v1.0, SSL v3.0 or SSL v2.0 cipher suites respectively.
DH
cipher suites using DH, including anonymous DH.
ADH
anonymous DH cipher suites.
AES
cipher suites using AES.
CAMELLIA
cipher suites using Camellia.
3DES
cipher suites using triple DES.
DES
cipher suites using DES (not triple DES).
RC4
cipher suites using RC4.
RC2
cipher suites using RC2.
IDEA
cipher suites using IDEA.
SEED
cipher suites using SEED.
MD5
cipher suites using MD5.
SHA1, SHA
cipher suites using SHA1.
aGOST
cipher suites using GOST R 34.10 (either 2001 or 94) for authenticaction (needs an engine supporting GOST algorithms).
aGOST01
cipher suites using GOST R 34.10-2001 authentication.
aGOST94
cipher suites using GOST R 34.10-94 authentication (note that R 34.10-94 standard has been expired so use GOST R 34.10-2001)
kGOST
cipher suites, using VKO 34.10 key exchange, specified in the RFC 4357.
GOST94
cipher suites, using HMAC based on GOST R 34.11-94.
GOST89MAC
cipher suites using GOST 28147-89 MAC instead of HMAC.