ssh-ecdsa.c

#include "includes.h"

#include <sys/types.h>

#include <openssl/bn.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>

#include <stdarg.h>
#include <string.h>

#include "xmalloc.h"
#include "buffer.h"
#include "compat.h"
#include "log.h"
#include "key.h"

const EVP_MD *
evp_from_key(const Key *key)
{
    switch (key->type) {
    case KEY_ECDSA:
    {
        int nid = EC_GROUP_get_curve_name(EC_KEY_get0_group(key->ecdsa));
        switch (nid) {
        case NID_X9_62_prime256v1:
            return EVP_sha256();
        case NID_secp384r1:
            return EVP_sha384();
        case NID_secp521r1:
            return EVP_sha512();
        }
    }
    }
    return NULL;
}

int
ssh_ecdsa_sign(const Key *key, u_char **sigp, u_int *lenp,
    const u_char *data, u_int datalen)
{
    ECDSA_SIG *sig;
    const EVP_MD *evp_md = evp_from_key(key);
    EVP_MD_CTX md;
    u_char digest[EVP_MAX_MD_SIZE];
    u_int len, dlen;
    Buffer b, bb;

    if (key == NULL || key->type != KEY_ECDSA || key->ecdsa == NULL) {
        pamsshagentauth_logerror("ssh_ecdsa_sign: no ECDSA key");
        return -1;
    }

    EVP_DigestInit(&md, evp_md);
    EVP_DigestUpdate(&md, data, datalen);
    EVP_DigestFinal(&md, digest, &dlen);

    sig = ECDSA_do_sign(digest, dlen, key->ecdsa);
    memset(digest, 'd', sizeof(digest));

    if (sig == NULL) {
        pamsshagentauth_logerror("ssh_ecdsa_sign: sign failed");
        return -1;
    }

    pamsshagentauth_buffer_init(&bb);
    if (pamsshagentauth_buffer_get_bignum2_ret(&bb, sig->r) == -1 ||
        pamsshagentauth_buffer_get_bignum2_ret(&bb, sig->s) == -1) {
        pamsshagentauth_logerror("couldn't serialize signature");
        ECDSA_SIG_free(sig);
        return -1;
    }

    pamsshagentauth_buffer_init(&b);
    pamsshagentauth_buffer_put_cstring(&b, key_ssh_name(key));
    pamsshagentauth_buffer_put_string(&b, pamsshagentauth_buffer_ptr(&bb),
        pamsshagentauth_buffer_len(&bb));

    len = pamsshagentauth_buffer_len(&b);
    if (lenp != NULL)
        *lenp = len;
    if (sigp != NULL) {
        *sigp = pamsshagentauth_xmalloc(len);
        memcpy(*sigp, pamsshagentauth_buffer_ptr(&b), len);
    }
    pamsshagentauth_buffer_free(&b);
    return 0;
}


int
ssh_ecdsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
    const u_char *data, u_int datalen)
{
    ECDSA_SIG *sig;
    const EVP_MD *evp_md = evp_from_key(key);
    EVP_MD_CTX md;
    u_char digest[EVP_MAX_MD_SIZE], *sigblob;
    u_int len, dlen;
    int rlen, ret;
    Buffer b;

    if (key == NULL || key->type != KEY_ECDSA || key->ecdsa == NULL) {
        pamsshagentauth_logerror("ssh_ecdsa_sign: no ECDSA key");
        return -1;
    }

    char *ktype;
    pamsshagentauth_buffer_init(&b);
    pamsshagentauth_buffer_append(&b, signature, signaturelen);

    ktype = pamsshagentauth_buffer_get_string(&b, NULL);
    pamsshagentauth_xfree(ktype);
    sigblob = pamsshagentauth_buffer_get_string(&b, &len);
    rlen = pamsshagentauth_buffer_len(&b);
    pamsshagentauth_buffer_free(&b);
    if (rlen != 0) {
        pamsshagentauth_logerror("ssh_ecdsa_verify: "
            "remaining bytes in signature %d", rlen);
        pamsshagentauth_xfree(sigblob);
        return -1;
    }

    /* parse signature */
    if ((sig = ECDSA_SIG_new()) == NULL)
        pamsshagentauth_fatal("ssh_ecdsa_verify: DSA_SIG_new failed");

    pamsshagentauth_buffer_init(&b);
    pamsshagentauth_buffer_append(&b, sigblob, len);
    if ((pamsshagentauth_buffer_get_bignum2_ret(&b, sig->r) == -1) ||
        (pamsshagentauth_buffer_get_bignum2_ret(&b, sig->s) == -1))
        pamsshagentauth_fatal("ssh_ecdsa_verify:"
            "pamsshagentauth_buffer_get_bignum2_ret failed");

    /* clean up */
    memset(sigblob, 0, len);
    pamsshagentauth_xfree(sigblob);

    /* sha256 the data */
    EVP_DigestInit(&md, evp_md);
    EVP_DigestUpdate(&md, data, datalen);
    EVP_DigestFinal(&md, digest, &dlen);

    ret = ECDSA_do_verify(digest, dlen, sig, key->ecdsa);
    memset(digest, 'd', sizeof(digest));

    ECDSA_SIG_free(sig);

    pamsshagentauth_verbose("ssh_ecdsa_verify: signature %s",
        ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
    return ret;
}