CURLOPT_HTTPSIG_KEY(3) Library Functions Manual CURLOPT_HTTPSIG_KEY(3)
NAME
CURLOPT_HTTPSIG_KEY - hex-encoded key for HTTP Message Signatures
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPSIG_KEY, char *key);
DESCRIPTION
This feature is experimental and may change before it is considered
stable. We advise against using it in production.
Pass a null-terminated string containing the hex-encoded private key or
shared secret used for RFC 9421 HTTP Message Signatures.
For ed25519, this is the 32-byte private seed (64 hex characters). For
hmac-sha256, this is the shared secret as hex; the decoded length is half
the number of hex digits, up to CURL_MAX_INPUT_LENGTH / 2 bytes (the same
upper bound as other libcurl string options).
PEM and other encodings are not supported; pass the raw key material as
hex.
Generating Ed25519 keys
With OpenSSL 3:
openssl genpkey -algorithm ED25519 -out k.pem
openssl pkey -in k.pem -text -noout | \
grep -A3 ^priv: | \
tr -cd '[:xdigit:]' > k.hex
The key.hex file is one line of 64 hexadecimal digits.
The application does not have to keep the string around after
setting this option.
Using this option multiple times makes the last set string
override the previous ones. Set it to NULL to disable its use
again.
DEFAULT
NULL
PROTOCOLS
This functionality affects http only
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/api");
curl_easy_setopt(curl, CURLOPT_HTTPSIG_ALGORITHM, CURLHTTPSIG_ED25519);
curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEY,
"9f8362f87a484a954e6e740c5b4c0e84"
"229139a20aa8ab56ff66586f6a7d29c5");
curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEYID, "my-key-id");
curl_easy_perform(curl);
}
}
AVAILABILITY
Added in curl 8.22.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_HTTPSIG_ALGORITHM(3), CURLOPT_HTTPSIG_KEYID(3)
libcurl 2026-10-18 CURLOPT_HTTPSIG_KEY(3)
curl 8.23.0 - Generated Sun Oct 18 16:01:06 CDT 2026