# SAT Solvers for Sage

One of the most efficient techniques for solving polynomial systems over $\mathbb{F}_2$ is to convert the problem to a satisfiability problem and to use a standard SAT solver. In the past, I have used CryptoMiniSat and either my own ANF to CNF converter scripts based on Gregory Bard’s ideas or PolyBoRi’s script.

However, this setup leaves much to be desired:

1. It’s all based on string parsing which has some overhead.
2. Usually the instances produced using PolyBoRi’s conversion method are faster to solve. However, as the number of variables per equation increase this method becomes essentially exponentially more expensive. Hence, a compromise between the two techniques is needed.
4. It all feels a bit duct taped and fragile, partly because the code is not shipped with Sage.

At #418 I just finished a much nicer interface to various SAT solvers. Here are some features.

### a proper C++ interface to CryptoMiniSat

The interface supports XOR clauses, an interface to various config options, conflict clause and learnt clause extraction. Here is an example run:

```sage: from sage.sat.solvers import CryptoMiniSat
sage: cms = CryptoMiniSat(verbosity=3)
sage: cms()
c N st 0 0 3 1 0 0 0 3 0 no data no data --
c Consolidated memory. Time: 0
c Flit: 0 Blit: 0 bXBeca: 0 bXProp: 0 Bins: 0 BRemL: 0 BRemN: 0 P: 0.0M T: 0.00
c Finding binary XORs T: 0.00 s found: 0
c Finding non-binary XORs: 0.00 s (found: 0, avg size: -nan)
c watched sorting time: 0.00
c calculated reachability. Time: 0.00
c Calc default polars - time: 0.00 s pos: 2 undec: 0 neg: 1
c ===============================================================
c types(t): F = full restart, N = normal restart
c types(t): S = simplification begin/end, E = solution found
c restart types(rt): st = static, dy = dynamic
c t rt Rest Confl Vars NormCls XorCls BinCls Learnts ClLits LtLits LGlueHist SGlueHist
c B st 0 0 3 1 0 0 0 3 0 no data no data --
c E st 1 0 0 1 0 0 0 3 0 no data no data --
c Verified 1 clauses.
c Verified 1 clauses.
(None, True, True, False)
```

Note that the first entry of the returned tuple is always None, because our SAT solver interface is one-based, i.e., the first variable is at index 1.

### a generic interface for various SAT solvers based on the DIMACS file format

… and instantiations of this for Glucose and RSat. Here is the code for the Glucose solver, to highlight how little thereof is needed to add new solvers.

```class Glucose(DIMACS):
command = "glucose_static -verb=2 {input} {output}"

def __call__(self, **kwds):
DIMACS.__call__(self)

for line in self._output:
if line.startswith("c"):
continue
if line.startswith("s"):
if "UNSAT" in line:
return False
try:
s = map(int, line[:-2].strip().split(" "))
s = (None,) + tuple(e>0 for e in s)
return s
except ValueError:
pass
return False
```

Of course, these solvers have the same interface as the CryptoMiniSat solver and hence one should be able to switch between these freely in highlevel code.

### a converter for Boolean Polynomials

The converter combines PolyBoRi’s ideas with Gregory’s. It’s not perfect, but a lot cleaner than what I used before. For polynomials with very few variables PolyBoRi’s conversion is used, for the rest we convert monomials first and then use XOR clauses (if available) to convert the linearised polynomials.

To give an example, below, various conversion strategies are compared for a small-scale AES instance.

```sage: F,s = mq.SR(1,2,4,4,gf2=True,polybori=True).polynomial_system()
sage: from sage.sat.solvers import CryptoMiniSat
sage: solver = CryptoMiniSat()

sage: from sage.sat.converters.polybori import CNFEncoder
sage: conv = CNFEncoder(solver, F.ring()) # the default strategy mixes
sage: %time _ = conv(F)
CPU times: user 0.10 s, sys: 0.00 s, total: 0.10 s
Wall time: 0.10 s
sage: %time _ = solver()
CPU times: user 0.60 s, sys: 0.00 s, total: 0.60 s
Wall time: 0.61 s

sage: solver = CryptoMiniSat()
sage: conv = CNFEncoder(solver, F.ring(), max_vars_sparse=0) # we can use only Greg's strategy by setting the cut-off to zero
sage: %time _ = conv(F)
CPU times: user 0.03 s, sys: 0.00 s, total: 0.03 s
Wall time: 0.03 s
sage: %time _ = solver()
CPU times: user 0.14 s, sys: 0.00 s, total: 0.14 s
Wall time: 0.14 s

sage: solver = CryptoMiniSat()
sage: conv = CNFEncoder(solver, F.ring(), max_vars_sparse=infinity) # or PolyBoRi all the way
sage: %time _ = conv(F)
CPU times: user 0.68 s, sys: 0.00 s, total: 0.68 s
Wall time: 0.68 s
sage: %time _ = solver()
CPU times: user 0.04 s, sys: 0.00 s, total: 0.04 s
Wall time: 0.04 s
```

Clearly, some tuning seems in order. Oh, I should also mention that the code is reasonably modular, so one can plug one’s own converter easily in higher level functions.

### Highlevel functions for Boolean polynomial systems

Firstly, there is a high-level solve command for Boolean polynomial systems. Continuing the above example:

```sage: from sage.sat.boolean_polynomials import solve as solve_sat
sage: solve_sat(F)
[{w121: 0, k100: 0, w161: 0, k062: 0, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 1, k101: 0, k001: 1, w122: 1, w102: 1, w162: 0, k061: 1, w142: 1, x100: 1, k022: 0, x113: 0, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 0, k150: 1, w143: 0, k173: 1, x112: 0, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 1, x110: 0, w170: 1, k063: 0, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 1, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 0, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 1, x143: 1, k110: 1, x163: 1, k012: 0, w133: 1, w113: 1, w173: 1, w153: 1, x102: 0, k033: 0, k163: 1, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 1, x162: 1, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 1, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}]
```

We can pass parameters to the solver and the converter by prefixing them with “s_” and “c_” respectively:

```sage: solve_sat(F, c_max_vars_sparse=0)
[{w121: 0, k100: 0, w161: 0, k062: 0, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 1, k101: 0, k001: 1, w122: 1, w102: 1, w162: 0, k061: 1, w142: 1, x100: 1, k022: 0, x113: 0, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 0, k150: 1, w143: 0, k173: 1, x112: 0, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 1, x110: 0, w170: 1, k063: 0, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 1, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 0, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 1, x143: 1, k110: 1, x163: 1, k012: 0, w133: 1, w113: 1, w173: 1, w153: 1, x102: 0, k033: 0, k163: 1, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 1, x162: 1, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 1, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}]
```

Let’s see if there are more than one solutions:

```sage: solve_sat(F, c_max_vars_sparse=0, n=infinity)
[{w121: 0, k100: 0, w161: 0, k062: 0, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 1, k101: 0, k001: 1, w122: 1, w102: 1, w162: 0, k061: 1, w142: 1, x100: 1, k022: 0, x113: 0, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 0, k150: 1, w143: 0, k173: 1, x112: 0, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 1, x110: 0, w170: 1, k063: 0, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 1, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 0, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 1, x143: 1, k110: 1, x163: 1, k012: 0, w133: 1, w113: 1, w173: 1, w153: 1, x102: 0, k033: 0, k163: 1, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 1, x162: 1, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 1, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}, {w121: 0, k100: 0, w161: 0, k062: 1, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 0, k101: 0, k001: 1, w122: 1, w102: 1, w162: 1, k061: 1, w142: 1, x100: 1, k022: 0, x113: 1, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 1, k150: 1, w143: 0, k173: 1, x112: 1, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 0, x110: 0, w170: 1, k063: 1, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 0, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 1, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 0, x143: 1, k110: 1, x163: 1, k012: 1, w133: 1, w113: 0, w173: 1, w153: 1, x102: 0, k033: 0, k163: 0, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 0, x162: 0, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 0, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}]
```

We can also swap the SAT solver:

```sage: solve_sat(F, solver=sage.sat.solvers.Glucose, n=infinity)
[{w121: 0, k100: 0, w161: 0, k062: 1, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 0, k101: 0, k001: 1, w122: 1, w102: 1, w162: 1, k061: 1, w142: 1, x100: 1, k022: 0, x113: 1, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 1, k150: 1, w143: 0, k173: 1, x112: 1, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 0, x110: 0, w170: 1, k063: 1, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 0, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 1, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 0, x143: 1, k110: 1, x163: 1, k012: 1, w133: 1, w113: 0, w173: 1, w153: 1, x102: 0, k033: 0, k163: 0, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 0, x162: 0, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 0, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}, {w121: 0, k100: 0, w161: 0, k062: 0, w141: 1, k021: 0, x120: 1, k141: 1, k041: 1, s001: 0, w101: 0, x160: 1, k101: 0, k001: 1, w122: 1, w102: 1, w162: 0, k061: 1, w142: 1, x100: 1, k022: 0, x113: 0, k160: 0, x133: 1, k042: 0, s002: 1, x153: 1, k140: 1, x173: 0, k002: 0, k120: 1, w123: 0, w103: 0, w163: 0, k150: 1, w143: 0, k173: 1, x112: 0, k023: 0, k153: 0, k043: 1, x132: 0, x152: 0, s003: 1, k133: 0, k003: 1, x172: 1, k113: 0, w130: 0, w110: 1, x110: 0, w170: 1, k063: 0, w150: 1, k172: 0, k161: 0, k030: 1, k152: 0, k050: 1, x131: 0, x151: 1, s010: 1, k132: 1, x130: 0, k010: 1, x171: 0, k112: 1, w131: 0, x140: 0, w111: 1, w171: 0, w151: 0, k072: 0, k031: 0, k171: 1, k151: 0, k051: 1, k121: 0, s011: 0, k131: 1, x170: 0, k011: 1, w132: 0, x150: 0, w112: 0, w100: 0, w172: 0, w152: 1, k071: 1, x111: 1, k032: 0, x103: 1, k170: 1, x123: 1, k052: 1, k111: 1, k130: 0, s012: 1, x143: 1, k110: 1, x163: 1, k012: 0, w133: 1, w113: 1, w173: 1, w153: 1, x102: 0, k033: 0, k163: 1, k053: 0, x122: 0, k143: 1, k123: 0, x142: 1, s013: 0, k103: 0, k013: 1, x162: 1, w140: 0, w120: 0, s000: 1, w160: 1, k073: 1, x101: 0, k040: 0, k070: 0, k162: 1, k060: 1, x121: 0, k142: 1, k122: 1, x141: 1, k000: 1, k102: 1, k020: 1, x161: 1}]
```

A second function allows to learn new polynomials using a SAT solver (only CryptoMiniSat for now). To vary the example, let’s do a higher order differential attack on seven rounds of PRESENT. Currently, we cannot solve this system within our patience span. However, we can learn some information about the equation system by interrupting the SAT solver after a while, similar to bounding the degree during a Gröbner basis computation.

```sage: attach present.py
sage: F,s = present_ia(PRESENT(80,7))
sage: F2 = F.eliminate_linear_variables(maxlength=1); F2
Polynomial Sequence with 30680 Polynomials in 7776 Variables
sage: from sage.sat.boolean_polynomials import learn as learn_sat
sage: H = learn_sat(F2, s_verbosity=3, s_maxrestarts=500, c_max_vars_sparse=4, c_cutting_number=6, max_length=5)
sage: H.ideal().interreduced_basis()[-1]
X00763 + X60763 + Y130760
```

The code needs review to get accepted into Sage and to spot bugs, perhaps improve the interface, documentation …

Update: fixed sourcecode to reflect interface changes.
Update2: fixed sourcecode.

## 8 thoughts on “SAT Solvers for Sage”

1. James McLaughlin says:

I can’t seem to get some of the example code to work correctly:

sage: solver = sage.sat.solvers.CryptoMiniSat()
simply gives me an error message. Is this supposed to be equivalent to
from sage.sat.solvers import CryptoMiniSat as solver
which seems to work fine – until

sage: conv = CNFEncoder(solver, F.ring())

gives me a very long error message including the line

TypeError: descriptor ‘var’ of ‘sage.sat.solvers.cryptominisat.cryptominisat.CryptoMiniSat’ object needs an argument

2. I fixed the source code for the first issue you reported. The second works fine for me.

3. James McLaughlin says:

Just trying to retest – and a line of code which worked before has mysteriously started giving error messages:

sage: F,s = mq.SR(1,2,4,4,gf2=True,polybori=True).polynomial_system()
—————————————————————————
ZeroDivisionError Traceback (most recent call last)

/home/linuxuser/Sage/sage-5.5-linux-64bit-ubuntu_12.04.1_lts-x86_64-Linux/ in ()

/home/linuxuser/Sage/sage-5.5-linux-64bit-ubuntu_12.04.1_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/crypto/mq/sr.pyc in polynomial_system(self, P, K, C)
2094
2095 if ciphertext is None:
-> 2096 ciphertext = self(plaintext, key)
2097 elif ciphertext is False:
2098 raise TypeError, “type %s of C not understood”%(type(ciphertext))

/home/linuxuser/Sage/sage-5.5-linux-64bit-ubuntu_12.04.1_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/crypto/mq/sr.pyc in __call__(self, P, K)
1357
-> 1358 P = SubBytes(P)
1359 if get_verbose() >= 2:
1360 print “R[%02d].s_box %s”%(self.n, self.hex_str_vector(P))

/home/linuxuser/Sage/sage-5.5-linux-64bit-ubuntu_12.04.1_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/crypto/mq/sr.pyc in sub_bytes(self, d)
669 “”"
670 d = self.state_array(d)
–> 671 return Matrix(self.base_ring(), d.nrows(), d.ncols(), [self.sub_byte(b) for b in d.list()])
672
673 def sub_byte(self, b):

/home/linuxuser/Sage/sage-5.5-linux-64bit-ubuntu_12.04.1_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/crypto/mq/sr.pyc in sub_byte(self, b)
712 if not b:
713 if not self._allow_zero_inversions:
–> 714 raise ZeroDivisionError, “A zero inversion occurred during an encryption or key schedule.”
715 else:
716 return self.sbox_constant()

ZeroDivisionError: A zero inversion occurred during an encryption or key schedule.
——————————————————————————–
I’ve actually uninstalled Sage and then reinstalled both it and CryptoMiniSat trying to fix this, but to no avail.

4. James McLaughlin says:

Ah – further experimentation seems to suggest that
from sage.sat.solvers import CryptoMiniSat
needs to come BEFORE
F,s = mq.SR(1,2,4,4,gf2=True,polybori=True).polynomial_system()
in the source. The reason the line was working before was that I’d typed it in while trying one of the source code examples earlier on the page.

5. James McLaughlin says:

All I can say is that
F,s = mq.SR(1,2,4,4,gf2=True,polybori=True).polynomial_system()
only works for me if I’ve previously typed
from sage.sat.solvers import CryptoMiniSat

Have you tried quitting Sage completely, restarting it and entering the code in “a converter for Boolean Polynomials” one line at a time?

6. Have you read the docs I pointed to? sr.polynomial_system() constructs a random system of equations which has a certain possibility of being unsatisfiable because it contains a zero inversion.

7. James McLaughlin says:

Okay, I’ve tried a few more times, and the explosion of error messages does indeed appear to be completely at random – so I was wrong about sage.sat.solvers import CryptoMiniSat being needed.

I’m guessing the line I was supposed to pick up on in the documentation was “If neither P, K nor C are provided, a random pair (P, K) will be generated.”, which would have indicated to me that this had a chance of causing the “inversion on the zero element”.