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- """
- An example implementation of STROBE. Doesn't include the key tree.
-
- Copyright (c) Mike Hamburg, Cryptography Research, 2016.
-
- I will need to contact legal to get a license for this; in the mean time it is
- for example purposes only.
- """
-
- from __future__ import absolute_import
- from Strobe.Keccak import KeccakF
-
- class AuthenticationFailed(Exception):
- """Thrown when a MAC fails."""
- pass
-
- I,A,C,T,M,K = 1<<0, 1<<1, 1<<2, 1<<3, 1<<4, 1<<5
-
- class Strobe(object):
- def __init__(self, proto, F = KeccakF(1600), security = 128, copy_of=None, doInit=True):
- if copy_of is None:
- self.pos = self.posbegin = 0
- self.I0 = None
- self.F = F
- self.R = F.nbytes - security//4
-
- # Domain separation doesn't use Strobe padding
- self.initialized = False
- self.st = bytearray(F.nbytes)
- domain = bytearray([1,self.R,1,0,1,12*8]) \
- + bytearray(b"STROBEv1.0.2")
- if doInit: self._duplex(domain, forceF=True)
-
- # cSHAKE separation is done.
- # Turn on Strobe padding and do per-proto separation
- self.R -= 2
- self.initialized = True
- if doInit: self.operate(A|M, proto)
-
- else:
- self.R,self.pos,self.posbegin,self.I0,self.F = \
- (copy_of.R,copy_of.pos,copy_of.posbegin,copy_of.I0,
- copy_of.F.copy())
- self.st = bytearray(copy_of.st)
- self.initialized = True
-
- def copy(self): return Strobe(None,copy_of=self)
- def deepcopy(self): return self.copy()
-
- def _runF(self):
- if self.initialized:
- self.st[self.pos] ^= self.posbegin
- self.st[self.pos+1] ^= 0x04
- self.st[self.R+1] ^= 0x80
- self.st = self.F(self.st)
- self.pos = self.posbegin = 0
-
- def _duplex(self, data, cbefore=False, cafter=False, forceF=False):
- assert not (cbefore and cafter)
-
- # Copy data, and convert string or int to bytearray
- # This converts an integer n to an array of n zeros
- data = bytearray(data)
-
- for i in range(len(data)):
- if cbefore: data[i] ^= self.st[self.pos]
- self.st[self.pos] ^= data[i]
- if cafter: data[i] = self.st[self.pos]
-
- self.pos += 1
- if self.pos == self.R: self._runF()
-
- if forceF and self.pos != 0: self._runF()
- return data
-
- def _beginOp(self, flags):
- # Adjust direction information so that sender and receiver agree
- if flags & T:
- if self.I0 is None: self.I0 = flags & I
- flags ^= self.I0
-
- # Update posbegin
- oldbegin, self.posbegin = self.posbegin, self.pos+1
-
- self._duplex([oldbegin,flags], forceF = flags&(C|K))
-
- def operate(self, flags, data, more=False, meta_flags=A|M, metadata=None):
- """
- STROBE main duplexing mode.
-
- Op is a byte which describes the operating mode, per the STROBE paper.
-
- Data is either a string or bytearray of data, or else a length. If it
- is given as a length, the data is that many bytes of zeros.
-
- If metadata is not None, first apply the given metadata in the given
- meta_op.
-
- STROBE operations are streamable. If more is true, this operation
- continues the previous operation. It therefore ignores metadata and
- doesn't use the beginOp code from the paper.
-
- Certain operations return data. If an operation returns no data
- (for example, AD and KEY don't return any data), it returns the empty
- byte array.
-
- The meta-operation might also return data. This is convenient for
- explicit framing (meta_op = 0b11010/0b11011) or encrypted explicit
- framing (meta_op = 0b11110/0b11111)
-
- If the operation is a MAC verification, this function returns the
- empty byte array (plus any metadata returned) on success, and throws
- AuthenticationFailed on failure.
- """
- assert not (flags & (K|1<<6|1<<7)) # Not implemented here
- meta_out = bytearray()
- if more:
- assert flags == self.cur_flags
- else:
- if metadata is not None:
- meta_out = self.operate(meta_flags, metadata)
- self._beginOp(flags)
- self.cur_flags = flags
-
- if (flags & (I|T) != (I|T)) and (flags & (I|A) != A):
- # Operation takes no input
- assert isinstance(data,int)
-
- # The actual processing code is just duplex
- cafter = (flags & (C|I|T)) == (C|T)
- cbefore = (flags & C) and not cafter
- processed = self._duplex(data, cbefore, cafter)
-
- # Determine what to do with the output.
- if (flags & (I|A)) == (I|A):
- # Return data to the application
- return meta_out + processed
-
- elif (flags & (I|T)) == T:
- # Return data to the transport.
- # A fancier implementation might send it directly.
- return meta_out + processed
-
- elif (flags & (I|A|T)) == (I|T):
- # Check MAC
- assert not more
- failures = 0
- for byte in processed: failures |= byte
- if failures != 0: raise AuthenticationFailed()
- return meta_out
-
- else:
- # Operation has no output data, but maybe output metadata
- return meta_out
-
- def ad (self,data, **kw): return self.operate(0b0010,data,**kw)
- def key (self,data, **kw): return self.operate(0b0110,data,**kw)
- def prf (self,data, **kw): return self.operate(0b0111,data,**kw)
- def send_clr(self,data, **kw): return self.operate(0b1010,data,**kw)
- def recv_clr(self,data, **kw): return self.operate(0b1011,data,**kw)
- def send_enc(self,data, **kw): return self.operate(0b1110,data,**kw)
- def recv_enc(self,data, **kw): return self.operate(0b1111,data,**kw)
- def send_mac(self,data=16,**kw): return self.operate(0b1100,data,**kw)
- def recv_mac(self,data ,**kw): return self.operate(0b1101,data,**kw)
- def ratchet (self,data=32,**kw): return self.operate(0b0100,data,**kw)
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