Succinct Non-Interactive Zero Knowledge for a von Neumann Architecture, Eli Ben-Sasson, Alessandro Chiesa, Eran Tromer, Madars Virza https://eprint.iacr.org/2013/879.pdf
Pinocchio: Nearly practical verifiable computation, Bryan Parno, Craig Gentry, Jon Howell, Mariana Raykova https://eprint.iacr.org/2013/279.pdf

Caution

Implementation from scratch in Go to understand the concepts. Do not use in production.

Not finished, implementing this in my free time to understand it better, so I don't have much time.

Usage

zkSnark
bn128 (more details: https://github.com/arnaucube/go-snark/tree/master/bn128)
Finite Fields operations
R1CS to QAP (more details: https://github.com/arnaucube/go-snark/tree/master/r1csqap)
Circuit Compiler

Example:

bn, err := bn128.NewBn128()
assert.Nil(t, err)

// new Finite Field
fqR := fields.NewFq(bn.R)

// new Polynomial Field
pf := r1csqap.NewPolynomialField(f)

// compile circuit and get the R1CS
flatCode := `
func test(x):
	aux = x*x
	y = aux*x
	z = x + y
	out = z + 5
`
// parse the code
parser := circuitcompiler.NewParser(strings.NewReader(flatCode))
circuit, err := parser.Parse()
assert.Nil(t, err)
fmt.Println(circuit)
// flat code to R1CS
fmt.Println("generating R1CS from flat code")
a, b, c := circuit.GenerateR1CS()

/*
now we have the R1CS from the circuit:
a == [[0 1 0 0 0 0] [0 0 0 1 0 0] [0 1 0 0 1 0] [5 0 0 0 0 1]]
b == [[0 1 0 0 0 0] [0 1 0 0 0 0] [1 0 0 0 0 0] [1 0 0 0 0 0]]
c == [[0 0 0 1 0 0] [0 0 0 0 1 0] [0 0 0 0 0 1] [0 0 1 0 0 0]]
*/


alphas, betas, gammas, zx := pf.R1CSToQAP(a, b, c)

// wittness = 1, 3, 35, 9, 27, 30
w := []*big.Int{b1, b3, b35, b9, b27, b30}

ax, bx, cx, px := pf.CombinePolynomials(w, alphas, betas, gammas)

hx := pf.DivisorPolinomial(px, zx)

// hx==px/zx so px==hx*zx
assert.Equal(t, px, pf.Mul(hx, zx))

// p(x) = a(x) * b(x) - c(x) == h(x) * z(x)
abc := pf.Sub(pf.Mul(ax, bx), cx)
assert.Equal(t, abc, px)
hz := pf.Mul(hx, zx)
assert.Equal(t, abc, hz)
	
div, rem := pf.Div(px, zx)
assert.Equal(t, hx, div)
assert.Equal(t, rem, r1csqap.ArrayOfBigZeros(4))

// calculate trusted setup
setup, err := GenerateTrustedSetup(bn, fqR, pf, len(w), circuit, alphas, betas, gammas, zx)
assert.Nil(t, err)
fmt.Println("t", setup.Toxic.T)

// piA = g1 * A(t), piB = g2 * B(t), piC = g1 * C(t), piH = g1 * H(t)
proof, err := GenerateProofs(bn, fqR, circuit, setup, hx, w)
assert.Nil(t, err)

assert.True(t, VerifyProof(bn, circuit, setup, proof))

Test

go test ./... -v

Thanks to @jbaylina, @bellesmarta, @adriamb for their explanations that helped to understand this a little bit. Also thanks to @vbuterin for all the published articles explaining the zkSNARKs.