When an encrypted communication with news server (option ServerX.Encryption) is active NZBGet and the news server use TLS/SSL protocol to exchange data in a secure way.
TLS/SSL specification defines many possible ciphers which can be used to encrypt data. The ciphers distinguish in algorithms and key lengths.
NZBGet can use two TLS/SSL libraries: OpenSSL and GnuTLS. The library can be selected during configuration step of building NZBGet.
When a TLS/SSL connection is created the so called TLS Handshake process is performed. During TLS Handshake the client (NZBGet) and the server (news server) choose the cipher for communication. By default the most secure cipher is selected. This cipher however may not give the best performance on your particular computer.
NZBGet provides an option ServerX.Cipher to manually select a cipher.
Example: on my SAT Receiver Vu+ choosing cipher RC4 has increased the speed from 2500KB/s to 3800KB/s. This should give you an idea how important the option is.
Many users have followed these instructions. Most tests show that the encryption/hash combination RC4/MD5 is the fastest on all machines (NOTE: this is summary from original article written in 2015, for updates see below). To use this cipher in NZBGet set option ServerX.Cipher to:
If NZBGet was compiled to use OpenSSL:
Server1.Cipher=RC4-MD5
If NZBGet was compiled to use GnuTLS:
Server1.Cipher=NONE:+VERS-TLS-ALL:+ARCFOUR-128:+RSA:+MD5:+COMP-ALL
If you want to learn more please read the whole article.
Modern Intel and ARM processors include hardware support for AES cipher. On such processors NZBGet shows much better performance when using AES than RC4. For example see this benchmark.
To use this cipher in NZBGet set option ServerX.Cipher to AES128-SHA or
AES256-SHA. These cipher strings are for usage with OpenSSL. For GnuTLS please
consult their documentation.
In the terminal execute the command
openssl ciphers -v
it prints the list of supported ciphers. Example:
root@VUPLUSDUO:~# openssl ciphers -v
DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1
DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) Mac=SHA1
AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA1
EDH-RSA-DES-CBC3-SHA SSLv3 Kx=DH Au=RSA Enc=3DES(168) Mac=SHA1
EDH-DSS-DES-CBC3-SHA SSLv3 Kx=DH Au=DSS Enc=3DES(168) Mac=SHA1
DES-CBC3-SHA SSLv3 Kx=RSA Au=RSA Enc=3DES(168) Mac=SHA1
DES-CBC3-MD5 SSLv2 Kx=RSA Au=RSA Enc=3DES(168) Mac=MD5
DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1
DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) Mac=SHA1
AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1
RC2-CBC-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC2(128) Mac=MD5
RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1
RC4-MD5 SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5
RC4-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5
EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH Au=RSA Enc=DES(56) Mac=SHA1
EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH Au=DSS Enc=DES(56) Mac=SHA1
DES-CBC-SHA SSLv3 Kx=RSA Au=RSA Enc=DES(56) Mac=SHA1
DES-CBC-MD5 SSLv2 Kx=RSA Au=RSA Enc=DES(56) Mac=MD5
EXP-EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH(512) Au=RSA Enc=DES(40) Mac=SHA1 export
EXP-EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH(512) Au=DSS Enc=DES(40) Mac=SHA1 export
EXP-DES-CBC-SHA SSLv3 Kx=RSA(512) Au=RSA Enc=DES(40) Mac=SHA1 export
EXP-RC2-CBC-MD5 SSLv3 Kx=RSA(512) Au=RSA Enc=RC2(40) Mac=MD5 export
EXP-RC2-CBC-MD5 SSLv2 Kx=RSA(512) Au=RSA Enc=RC2(40) Mac=MD5 export
EXP-RC4-MD5 SSLv3 Kx=RSA(512) Au=RSA Enc=RC4(40) Mac=MD5 export
EXP-RC4-MD5 SSLv2 Kx=RSA(512) Au=RSA Enc=RC4(40) Mac=MD5 export
First column is the cipher suite name. This name must be used in NZBGet in option ServerX.Cipher.
The second column indicates the SSL version (v2 or v3) where the cipher suite can be used. Some cipher suits can be used in both SSL versions and therefore have two rows in the list for the same cipher suite name.
Column Kx is the algorithm used for key exchange.
Column Au is the algorithm for authentication.
Column Enc is the bulk encryption algorithm used to encrypt the message stream.
Column Mac is the message authentication code (MAC) algorithm used to create the message digest, a cryptographic hash of each block of the message stream.
For example take a detailed look at the first row DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1 This cipher suite name is DHE-RSA-AES256-SHA. It is for SSL version 3, the key exchange algorithm (Kx) is DH, the authentication algorithm (Au) is RSA, the encryption algorithm (Enc) is AES(256), the message authentication code algorithm (Mac) is SHA1.
Kx (key exchange) and Au (authentication) are performed only during the establishing connection and are therefore not relevant for performance.
Enc (encryption algorithm) and Mac (message authentication code algorithm) are used to encrypt/decrypt the data stream and have direct impact on performance.
Now we must choose a cipher suite with the fastest Enc and Mac ciphers. Lets write down all Enc and Mac algorithms listed in the table:
Enc: AES(256), 3DES(168), AES(128), RC2(128), RC4(128). I intentionally skipped the ciphers with key length less than 128 bit (DES(56), RC2(40), etc.); they cannot be considered secure nowadays.
Mac: SHA1, MD5.
The next step is to test the speed of Enc ciphers AES(256), 3DES(168), AES(128), RC2(128), RC4(128) and Mac algorithms SHA1, MD5 and choose the fastest combination of both.
In the terminal execute the command
openssl speed
NOTE: to get correct results make sure the computer is not used for any other tasks during testing.
The command tests all ciphers (this take several minutes), then prints the summary. Example from my SAT receiver:
root@VUPLUSDUO:~# openssl speed
<STRIPPED INDIVIDUAL TEST RESULTS, SHOWING ONLY THE SUMMARY>
The 'numbers' are in 1000s of bytes per second processed.
type 16 bytes 64 bytes 256 bytes 1024 bytes 8192 bytes
md2 202.16k 430.91k 594.79k 648.19k 666.28k
mdc2 0.00 0.00 0.00 0.00 0.00
md4 1582.24k 5385.28k 14451.80k 24957.61k 31787.15k
md5 1102.43k 3746.60k 10390.36k 18673.66k 24117.25k
hmac(md5) 1505.20k 4865.69k 12335.87k 20036.61k 24545.86k
sha1 1187.80k 3436.65k 7509.85k 10738.99k 12416.34k
rmd160 991.07k 2762.05k 5750.44k 7885.14k 8863.74k
rc4 13628.26k 15201.09k 15710.89k 15851.86k 15867.90k
des cbc 2228.90k 2314.86k 2338.47k 2353.15k 2367.49k
des ede3 851.43k 863.81k 866.82k 867.33k 860.30k
idea cbc 0.00 0.00 0.00 0.00 0.00
seed cbc 0.00 0.00 0.00 0.00 0.00
rc2 cbc 2910.75k 3036.48k 3067.90k 3077.46k 3067.24k
rc5-32/12 cbc 0.00 0.00 0.00 0.00 0.00
blowfish cbc 5245.97k 5618.39k 5726.29k 5750.10k 5758.98k
cast cbc 5221.43k 5609.28k 5718.70k 5749.08k 5748.05k
aes-128 cbc 4438.49k 4791.91k 4902.49k 4932.95k 4931.58k
aes-192 cbc 3914.24k 4194.24k 4280.06k 4297.73k 4303.53k
aes-256 cbc 3501.63k 3730.43k 3793.24k 3810.99k 3796.62k
camellia-128 cbc 0.00 0.00 0.00 0.00 0.00
camellia-192 cbc 0.00 0.00 0.00 0.00 0.00
camellia-256 cbc 0.00 0.00 0.00 0.00 0.00
sha256 894.82k 2050.47k 3536.71k 4378.20k 4745.90k
sha512 258.83k 1033.47k 1493.79k 2049.37k 2299.22k
aes-128 ige 4502.86k 5114.15k 5349.89k 5418.67k 5428.57k
aes-192 ige 4006.06k 4482.37k 4586.50k 4627.80k 4628.48k
aes-256 ige 3550.93k 3919.27k 4038.83k 4066.65k 4071.42k
<STRIPPED TEST RESULTS FOR KEY EXCHANGE ALGORITHMS>
The table shows more algorithms than we are interested in. Just keep only the rows for algorithms we can use (AES(256), 3DES(168), AES(128), RC2(128), RC4(128) for Enc and SHA1, MD5 for Mac). The speed results table shrinks to:
The 'numbers' are in 1000s of bytes per second processed.
type 16 bytes 64 bytes 256 bytes 1024 bytes 8192 bytes
md5 1102.43k 3746.60k 10390.36k 18673.66k 24117.25k
sha1 1187.80k 3436.65k 7509.85k 10738.99k 12416.34k
rc4 13628.26k 15201.09k 15710.89k 15851.86k 15867.90k
des cbc 2228.90k 2314.86k 2338.47k 2353.15k 2367.49k
des ede3 851.43k 863.81k 866.82k 867.33k 860.30k
rc2 cbc 2910.75k 3036.48k 3067.90k 3077.46k 3067.24k
aes-128 cbc 4438.49k 4791.91k 4902.49k 4932.95k 4931.58k
aes-256 cbc 3501.63k 3730.43k 3793.24k 3810.99k 3796.62k
aes-128 ige 4502.86k 5114.15k 5349.89k 5418.67k 5428.57k
aes-256 ige 3550.93k 3919.27k 4038.83k 4066.65k 4071.42k
I don’t really know the difference between aes cbc and aes ige so I kept both in the table. Another question is what column to look at. Some ciphers have better speeds for larger block sizes whereas other ciphers don’t really care. I don’t know actually what block size is more important, so I looked at the middle column 256 bytes (not very scientifically I guess).
From all Enc-algorithms (AES(256), 3DES(168), AES(128), RC2(128), RC4(128)) we see that RC4 provides by far the best speed.
From two Mac-algorithms (SHA1, MD5) MD5 is the fastest.
Now take a look at the cipher list (first table) and find the rows where Enc=RC4 and Mac=MD5 (I ignored Enc-ciphers with less than 128 bits keys):
RC4-MD5 SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5
RC4-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5
The first column is the cipher suite name - it’s RC4-MD5. This is the cipher with best performance. Just test it in NZBGet. Set option ServerX.Cipher:
Server1.Cipher=RC4-MD5
Now test the download speed in NZBGet. On my SAT Receiver Vu+ choosing cipher “RC4-MD5” has increased the speed from 2500KB/s to 3800KB/s. Not bad, isn’t it?
I have not made any performance tests using GnuTLS.
It has similar commands “gnutls-cli –list”, “gnutls-cli –benchmark-ciphers” and “gnutls-cli –benchmark-tls-ciphers”. Please note that the benchmark commands require at least version 3.0.13 of GnuTLS. Use “gnutls-cli –help” to print the list of supported options.
GnuTLS has a very different syntax to specify the ciphers to use. For example to select RC4 as Enc-algorithm and MD5 as Mac-algorithm you should set the option ServerX.Cipheras:
Server1.Cipher=NONE:+VERS-TLS-ALL:+ARCFOUR-128:+RSA:+MD5:+COMP-ALL
For detailed explanation what does it mean see Priority strings in GnuTLS documentation.