---
title: "DSA Signature/Verification"
source_url: https://dev.digicert.com/trustcore-sdk/crypto-interface/asymmetric-key-algorithms/dsa-signature-verification.html
---

DSA is analogous to [ECDSA](https://dev.digicert.com/md/trustcore-sdk/crypto-interface/asymmetric-key-algorithms/ecdsa-signature-verification.md), except that computations are done in a finite field. Like ECDSA, the resulting signature is made up of two values, *r* and *s*. The Crypto Interface APIs do not perform any message digesting. The application is required to handle any steps before the DSA signing step.

To sign, call:

```c
CRYPTO_INTERFACE_DSA_computeSignatureAux(g_pRandomContext, pPrivKey, pDigest, digestLen, NULL, &pR, &rLen, &pS, &sLen, NULL);
```

Buffers are allocated to hold *r* and *s* in a big-endian byte array form, and `pR` and `pS` are set to their locations. In the middle, pass `NULL` so that verification is not performed immediately after signing, and the final `NULL` is for the `vlong` queue. To verify, call:

```c
CRYPTO_INTERFACE_DSA_verifySignatureAux(pPubKey, pDigest, digestLen, pR, rLen, pS, sLen, &isValid, NULL);
```

Here, `isValid` will be set to `TRUE` if it is a valid signature, and `FALSE` otherwise.


> **Important**
>
> Be sure to check that both the return status is `OK` and `isValid` is equal to `TRUE` before accepting that the signature is valid.