Code snippet for converting between OpenSSL types and SecKeyRefs. Hacky, but it worked for my needs.

gistfile1.txt

uint8_t get_EC_curve(const EC_key_t ec)
{
    int nid;

    nid = EC_GROUP_get_curve_name(EC_KEY_get0_group(ec));
    return get_ec_curve_type(nid);
}

static EC_KEY *SecKeyToOpenSSLKey(SecKeyRef secKey, int public) {
    CFErrorRef error;
    CFDataRef data = SecKeyCopyExternalRepresentation(secKey, &error);
    if (!data) {
        fprintf(stderr, "unable to copy external representation");
        return NULL;
    }
    EC_KEY *ec;
    if ((ec = EC_KEY_new_by_curve_name(
                    get_ec_curve_nid(get_EC_curve_darwin(secKey)))) == NULL) {
        log_ssl_err("EC_KEY_new_by_curve_name failed");
        return NULL;
    }
    CFIndex keylen = CFDataGetLength(data);
    const unsigned char *buf = CFDataGetBytePtr(data);
    if (public) {
        if (!o2i_ECPublicKey(&ec, &buf, keylen)) {
            fprintf(stderr, "o2i_ECPublicKey failed");
            EC_KEY_free(ec);
            return NULL;
        }
    } else {
        CFDataRef derData;
        OSStatus status = SecItemExport(secKey, kSecFormatOpenSSL, 0, NULL, &derData);
        if (status != noErr) {
            fprintf(stderr, "unable to export: %d", status);
            return NULL;
        }
        unsigned char *defBuf = CFDataGetBytePtr(derData);
        if (!d2i_ECPrivateKey(&ec, &defBuf, CFDataGetLength(derData))) {
            fprintf(stderr, "d2i_ECPrivateKey failed");
            EC_KEY_free(ec);
            CFRelease(derData);

            return NULL;
        }
        CFRelease(derData);
    }
    if (!EC_KEY_check_key(ec)) {
        fprintf(stderr, "Conversion Failed");
        EC_KEY_free(ec);
    }
    return ec;
}

static SecKeyRef OpenSSLKeyToSecKey(EC_KEY *key, int public) {
    if (public) {
        size_t keylen;
        if ((keylen = i2o_ECPublicKey(key, NULL)) == 0) {
            log0(0, 0, 0, "error getting size of EC key");
            return 0;
        }
        unsigned char *buf = safe_malloc(keylen);
        unsigned char *tmp = buf;
        // After this call, tmp points to (buf + keylen),
        // but the exported key lives at buf
        if (!i2o_ECPublicKey(key, &tmp)) {
            fprintf(stderr, "i2o_ECPublicKey failed");
            free(buf);
            return NULL;
        }
        CFDataRef data = CFDataCreateWithBytesNoCopy(NULL, buf, keylen, kCFAllocatorMalloc);
        CFMutableDictionaryRef dict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks , &kCFTypeDictionaryValueCallBacks);
        CFDictionaryAddValue(dict, kSecAttrKeyType, kSecAttrKeyTypeECDSA);
        CFDictionaryAddValue(dict, kSecAttrKeyClass, kSecAttrKeyClassPublic);
        CFErrorRef error;
        SecKeyRef key = SecKeyCreateWithData(data, dict, &error);
        CFRelease(data);
        CFRelease(dict);
        return key;
    } else {
        size_t keylen;
        if ((keylen = i2d_ECPrivateKey(key, NULL)) == 0) {
            fprintf(stderr, "error getting size of EC key");
            return 0;
        }
        unsigned char *buf = safe_malloc(keylen);
        unsigned char *tmp = buf;
        // After this call, tmp points to (buf + keylen),
        // but the exported key lives at buf
        if (!i2d_ECPrivateKey(key, &tmp)) {
            fprintf(stderr, "i2o_ECPublicKey failed");
            free(buf);
            return NULL;
        }
        CFDataRef data = CFDataCreateWithBytesNoCopy(NULL, buf, keylen, kCFAllocatorMalloc);
        CFArrayRef array;
        SecItemImportExportKeyParameters params;
        bzero(&params, sizeof(params));
        params.keyAttributes = CFArrayCreate(NULL, &kSecAttrIsExtractable, 1, &kCFTypeArrayCallBacks);
        OSStatus status = SecItemImport(data, NULL, NULL, NULL, 0, &params, NULL, &array);
        CFRelease(params.keyAttributes);
        if (status != noErr) {
            fprintf(stderr, "SecItemImport failed %d", status);
            return NULL;
        }
        SecKeyRef key = CFArrayGetValueAtIndex(array, 0);
        CFRetain(key);
        CFRelease(array);
        return key;
    }
}