An algorithm is presented for computing the determinant and the characteristic polynomial of a matrix $A$ over an arbitrary commutative ring R. The algorithm uses $O(n^ω)$ ring additions, subtractions and multiplications, where $ω>2$ is a feasible exponent for matrix multiplication, that is, such that two $n\times n$ matrices over R can be multiplied using $O(n^ω)$ ring operations. The algorithm involves no division and no zero test, and its control depends only on $n$: for each $n$ it is a straight-line program. The approach combines a polynomial matrix point of view and a block Krylov point of view on the characteristic polynomial, which makes Strassen's elimination of divisions efficient. A bivariate matrix $λI-L(t)$, obtained from $A$ by a homotopy, is compressed in $\log n$ steps, each of which halves the dimension while only doubling the degree in $λ$. The cost of the homotopy is controlled by truncating the power series in $t$ at an order that only grows with the compression steps, from a constant to $n$.

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