---
name: "sc_pkcs15_compute_signature"
section: "3"
platform: "linux"
package: "libopensc1-dev"
version: "0.9.6-1"
release: "Debian 3.1 (Sarge)"
platforms: ["linux"]
url: "https://new.carta.tech/sc_pkcs15_compute_signature"
---

# sc\_pkcs15\_compute\_signature(3)

compute digitial signature

## NAME

sc\_pkcs15\_compute\_signature - compute digitial signature

## SYNOPSIS

```
#include <opensc.h>

int sc_pkcs15_compute_signature(struct sc_pkcs15_card *p15card,
                   const struct sc_pkcs15_object *obj,
                   unsigned long flags, const u8 *in, size_t inlen,
                   u8 *out, size_t outlen);
```

## DESCRIPTION

This function digitally signs the data pointed to by **in**, using the key identified by **obj**, and places the resulting signature in the buffer pointed to by **out**. The signature operation will be performed on the smart card identified by **p15card**.

Currently, only RSA signatures are supported.

The **flags** argument provides additional information on how the signature is to be computed. In particular, it specifies how the input data should be padded:

- **SC\_ALGORITHM\_RSA\_RAW**

  requests that the card should sign the provided data as-is. The length of the input data must match the modulus length of the key.

- **SC\_ALGORITHM\_RSA\_PAD\_PKCS1**

  requests that the card should sign the provided data, padding it according to the padding algorithm specified in PKCS #1.

-

  The input data must be the output of a digest (hash) function. As PKCS #1 padding includes an identifier of the hash algorithm used, the **flags** argument must indicate the hash algorithm used, by ORing **SC\_ALGORITHM\_RSA\_PAD\_PKCS1** with one of the following values: **SC\_ALGORITHM\_RSA\_HASH\_MD5**, **SC\_ALGORITHM\_RSA\_HASH\_SHA1**, **SC\_ALGORITHM\_RSA\_HASH\_RIPEMD160**, **SC\_ALGORITHM\_RSA\_HASH\_MD5\_SHA1**,**or** **SC\_ALGORITHM\_RSA\_HASH\_NONE**.

-

  In any of these cases, the length of the input data must match the digest length of the hash algorithm. In the first 3 cases, the respective digestinfo is prepended to the input data (the hash), in the last 2 cases, no digestinfo is prepended.

- **SC\_ALGORITHM\_RSA\_PAD\_ANSI**

  requests that the card should use ANSI padding when signing the provided data.

- **SC\_ALGORITHM\_RSA\_PAD\_ISO9796**

  requests that the card should use ISO 9796 padding when signing the provided data.

## Card Driver Considerations

Depending on the card's capabilities, **sc\_pkcs15\_compute\_signature** is able to process the provided data so that it is in a form suitable for the card. For instance, if a smart card supports raw RSA only, the function will have to add the required padding before passing it to the card driver. Conversely, an error should be returned if the card supports only PKCS #1 padding with a specific set of hash algorithms.

## RETURN VALUE

If an error occurred, a negative error code is returned, as described in **sc\_error**(3). Otherwise, the function will return the size of the signature.

## SEE ALSO

**sc\_pkcs15\_decipher**(3), **sc\_compute\_signature**(3).

## AUTHOR

This manual page was written by Olaf Kirch \<okir@suse.de\>