RFR(L): 8069539: RSA acceleration (original) (raw)

Florian Weimer fweimer at redhat.com
Mon Mar 23 13:59:46 UTC 2015

On 03/20/2015 11:45 PM, Viswanathan, Sandhya wrote:

Hi Florian,

My thoughts on this are as follows: BigInteger.squareToLen is a private method and not a public method. The length calculation code in Java version of this method does not have the overflow check and the intrinsic follows the Java code. private static final int[] squareToLen(int[] x, int len, int[] z) { ... int zlen = len << 1; if (z == null || z.length < zlen) z = new int[zlen]; ... }

The difference is that the Java code will still perform the bounds checks on each array access, I think, so even if zlen turns out negative (and thus no reallocation happens), damage from out-of-bounds accesses will be non-existent.

Also the underlying array in BigInteger cannot be greater than MAXMAGLENGTH which is defined as:

private static final int MAXMAGLENGTH = Integer.MAXVALUE / Integer.SIZE + 1; // (1 << 26) So zlen calculation cannot overflow as int array x and its length len is coming from a BigInteger array.

Maybe can you add this as a comment to the intrinsic? I think this would be a useful addition, especially if at some point in the future, someone else uses your code as a template to implement their own intrinsic.

Similarly mulAdd is a package private method and its inputs are allocated or verified at call sites.

Same here.

-- Florian Weimer / Red Hat Product Security

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