---
name: "libressl-EVP_PKEY_CTX_set_tls1_prf_md"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-EVP_PKEY_CTX_set_tls1_prf_md"
---

# libressl-EVP\_PKEY\_CTX\_set\_tls1\_prf\_md(3)

TLS PRF key derivation algorithm

## NAME

**EVP\_PKEY\_CTX\_set\_tls1\_prf\_md**, **EVP\_PKEY\_CTX\_set1\_tls1\_prf\_secret**, **EVP\_PKEY\_CTX\_add1\_tls1\_prf\_seed** – TLS PRF key derivation algorithm

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#include \<openssl/evp.h\>**

**#include \<openssl/kdf.h\>**

*int*\

**EVP\_PKEY\_CTX\_set\_tls1\_prf\_md**(*EVP\_PKEY\_CTX \*pctx*, *const EVP\_MD \*md*);

*int*\

**EVP\_PKEY\_CTX\_set1\_tls1\_prf\_secret**(*EVP\_PKEY\_CTX \*pctx*, *unsigned char \*sec*, *int seclen*);

*int*\

**EVP\_PKEY\_CTX\_add1\_tls1\_prf\_seed**(*EVP\_PKEY\_CTX \*pctx*, *unsigned char \*seed*, *int seedlen*);

## DESCRIPTION

The EVP\_PKEY\_TLS1\_PRF algorithm implements the PRF key derivation function for TLS. It has no associated private key and only implements key derivation using EVP\_PKEY\_derive(3).

**EVP\_PKEY\_set\_tls1\_prf\_md**() sets the message digest associated with the TLS PRF. EVP\_md5\_sha1(3) is treated as a special case which uses the PRF algorithm using both MD5 and SHA-1 as used in TLS 1.0 and 1.1.

**EVP\_PKEY\_CTX\_set\_tls1\_prf\_secret**() sets the secret value of the TLS PRF to *seclen* bytes of the buffer *sec*. Any existing secret value is replaced and any seed is reset.

**EVP\_PKEY\_CTX\_add1\_tls1\_prf\_seed**() sets the seed to *seedlen* bytes of *seed*. If a seed is already set it is appended to the existing value.

## STRING CTRLS

The TLS PRF also supports string based control operations using EVP\_PKEY\_CTX\_ctrl\_str(3). The *type* parameter "md" uses the supplied *value* as the name of the digest algorithm to use. The *type* parameters "secret" and "seed" use the supplied *value* parameter as a secret or seed value. The names "hexsecret" and "hexseed" are similar except they take a hex string which is converted to binary.

## NOTES

All these functions are implemented as macros.

A context for the TLS PRF can be obtained by calling:

```
 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
```

The digest, secret value and seed must be set before a key is derived or an error occurs.

The total length of all seeds cannot exceed 1024 bytes in length: this should be more than enough for any normal use of the TLS PRF.

The output length of the PRF is specified by the length parameter in the EVP\_PKEY\_derive(3) function. Since the output length is variable, setting the buffer to NULL is not meaningful for the TLS PRF.

## RETURN VALUES

All these functions return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm.

## EXAMPLES

This example derives 10 bytes using SHA-256 with the secret key "secret" and seed value "seed":

```
 EVP_PKEY_CTX *pctx;
 unsigned char out[10];
 size_t outlen = sizeof(out);
 pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
 if (EVP_PKEY_derive_init(pctx) <= 0)
     /* Error */
 if (EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_sha256()) <= 0)
     /* Error */
 if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, "secret", 6) <= 0)
     /* Error */
 if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, "seed", 4) <= 0)
     /* Error */
 if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
     /* Error */
```

## SEE ALSO

EVP\_PKEY\_CTX\_ctrl\_str(3), EVP\_PKEY\_CTX\_new(3), EVP\_PKEY\_derive(3)

## HISTORY

These functions first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 7.6.