Class BaseMAC
- java.lang.Object
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- net.schmizz.sshj.transport.mac.BaseMAC
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- All Implemented Interfaces:
MAC
- Direct Known Subclasses:
HMACMD5
,HMACMD596
,HMACRIPEMD160
,HMACSHA1
,HMACSHA196
,HMACSHA2256
,HMACSHA2512
public class BaseMAC extends java.lang.Object implements MAC
Base class forMAC
implementations based on the JCE provider.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description byte[]
doFinal()
byte[]
doFinal(byte[] input)
void
doFinal(byte[] buf, int offset)
int
getBlockSize()
void
init(byte[] key)
boolean
isEtm()
Indicates that an Encrypt-Then-Mac algorithm was selected.private byte[]
resizeToHashSize(byte[] buf)
void
update(byte[] foo)
void
update(byte[] foo, int s, int l)
void
update(long i)
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Method Detail
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resizeToHashSize
private byte[] resizeToHashSize(byte[] buf)
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getBlockSize
public int getBlockSize()
- Specified by:
getBlockSize
in interfaceMAC
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isEtm
public boolean isEtm()
Description copied from interface:MAC
Indicates that an Encrypt-Then-Mac algorithm was selected.This has the following implementation details. 1.5 transport: Protocol 2 Encrypt-then-MAC MAC algorithms
OpenSSH supports MAC algorithms, whose names contain "-etm", that perform the calculations in a different order to that defined in RFC 4253. These variants use the so-called "encrypt then MAC" ordering, calculating the MAC over the packet ciphertext rather than the plaintext. This ordering closes a security flaw in the SSH transport protocol, where decryption of unauthenticated ciphertext provided a "decryption oracle" that could, in conjunction with cipher flaws, reveal session plaintext.
Specifically, the "-etm" MAC algorithms modify the transport protocol to calculate the MAC over the packet ciphertext and to send the packet length unencrypted. This is necessary for the transport to obtain the length of the packet and location of the MAC tag so that it may be verified without decrypting unauthenticated data.
As such, the MAC covers:
mac = MAC(key, sequence_number || packet_length || encrypted_packet)
where "packet_length" is encoded as a uint32 and "encrypted_packet" contains:
byte padding_length byte[n1] payload; n1 = packet_length - padding_length - 1 byte[n2] random padding; n2 = padding_length
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