s2n_stuffer_pem.c

/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

#include <openssl/evp.h>
#include <string.h>

#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "utils/s2n_safety.h"

#define S2N_PEM_DELIMITER_CHAR        '-'
#define S2N_PEM_DELIMITER_TOKEN       "--"
#define S2N_PEM_DELIMITER_MIN_COUNT   2
#define S2N_PEM_DELIMITER_MAX_COUNT   64
#define S2N_PEM_BEGIN_TOKEN           "BEGIN "
#define S2N_PEM_END_TOKEN             "END "
#define S2N_PEM_PKCS1_RSA_PRIVATE_KEY "RSA PRIVATE KEY"
#define S2N_PEM_PKCS1_EC_PRIVATE_KEY  "EC PRIVATE KEY"
#define S2N_PEM_PKCS8_PRIVATE_KEY     "PRIVATE KEY"
#define S2N_PEM_DH_PARAMETERS         "DH PARAMETERS"
#define S2N_PEM_EC_PARAMETERS         "EC PARAMETERS"
#define S2N_PEM_CERTIFICATE           "CERTIFICATE"
#define S2N_PEM_CRL                   "X509 CRL"

static S2N_RESULT s2n_stuffer_pem_read_delimiter_chars(struct s2n_stuffer *pem)
{
    RESULT_ENSURE_REF(pem);
    RESULT_ENSURE(s2n_stuffer_data_available(pem) >= S2N_PEM_DELIMITER_MIN_COUNT,
            S2N_ERR_INVALID_PEM);

    /* Skip any number of chars until a "--" is reached.
     * We use "--" instead of "-" to account for dashes that appear in comments.
     * We do not accept comments that contain "--".
     */
    RESULT_GUARD_POSIX(s2n_stuffer_skip_read_until(pem, S2N_PEM_DELIMITER_TOKEN));
    RESULT_GUARD_POSIX(s2n_stuffer_rewind_read(pem, strlen(S2N_PEM_DELIMITER_TOKEN)));

    /* Ensure between 2 and 64 '-' chars at start of line. */
    RESULT_GUARD_POSIX(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMITER_CHAR,
            S2N_PEM_DELIMITER_MIN_COUNT, S2N_PEM_DELIMITER_MAX_COUNT, NULL));

    return S2N_RESULT_OK;
}

static int s2n_stuffer_pem_read_encapsulation_line(struct s2n_stuffer *pem, const char *encap_marker,
        const char *keyword)
{
    POSIX_GUARD_RESULT(s2n_stuffer_pem_read_delimiter_chars(pem));

    /* Ensure next string in stuffer is "BEGIN " or "END " */
    POSIX_GUARD(s2n_stuffer_read_expected_str(pem, encap_marker));

    /* Ensure next string is stuffer is the keyword (Eg "CERTIFICATE", "PRIVATE KEY", etc) */
    POSIX_GUARD(s2n_stuffer_read_expected_str(pem, keyword));

    /* Ensure between 2 and 64 '-' chars at end of line */
    POSIX_GUARD(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMITER_CHAR, S2N_PEM_DELIMITER_MIN_COUNT,
            S2N_PEM_DELIMITER_MAX_COUNT, NULL));

    /* Check for missing newline between dashes case: "-----END CERTIFICATE----------BEGIN CERTIFICATE-----" */
    if (strncmp(encap_marker, S2N_PEM_END_TOKEN, strlen(S2N_PEM_END_TOKEN)) == 0
            && s2n_stuffer_peek_check_for_str(pem, S2N_PEM_BEGIN_TOKEN) == S2N_SUCCESS) {
        /* Rewind stuffer by 2 bytes before BEGIN, so that next read will find the dashes before the BEGIN */
        POSIX_GUARD(s2n_stuffer_rewind_read(pem, S2N_PEM_DELIMITER_MIN_COUNT));
    }

    /* Skip newlines and other whitespace that may be after the dashes */
    return s2n_stuffer_skip_whitespace(pem, NULL);
}

static int s2n_stuffer_pem_read_begin(struct s2n_stuffer *pem, const char *keyword)
{
    return s2n_stuffer_pem_read_encapsulation_line(pem, S2N_PEM_BEGIN_TOKEN, keyword);
}

static int s2n_stuffer_pem_read_end(struct s2n_stuffer *pem, const char *keyword)
{
    return s2n_stuffer_pem_read_encapsulation_line(pem, S2N_PEM_END_TOKEN, keyword);
}

static int s2n_stuffer_pem_read_contents(struct s2n_stuffer *pem, struct s2n_stuffer *asn1)
{
    s2n_stack_blob(base64__blob, 64, 64);
    struct s2n_stuffer base64_stuffer = { 0 };
    POSIX_GUARD(s2n_stuffer_init(&base64_stuffer, &base64__blob));

    while (1) {
        /* We need a byte... */
        POSIX_ENSURE(s2n_stuffer_data_available(pem) >= 1, S2N_ERR_STUFFER_OUT_OF_DATA);

        /* Peek to see if the next char is a dash, meaning end of pem_contents */
        uint8_t c = pem->blob.data[pem->read_cursor];
        if (c == '-') {
            break;
        }
        /* Else, move read pointer forward by 1 byte since we will be consuming it. */
        pem->read_cursor += 1;

        /* Skip non-base64 characters */
        if (!s2n_is_base64_char(c)) {
            continue;
        }

        /* Flush base64_stuffer to asn1 stuffer if we're out of space, and reset base64_stuffer read/write pointers */
        if (s2n_stuffer_space_remaining(&base64_stuffer) == 0) {
            POSIX_GUARD(s2n_stuffer_read_base64(&base64_stuffer, asn1));
            POSIX_GUARD(s2n_stuffer_rewrite(&base64_stuffer));
        }

        /* Copy next char to base64_stuffer */
        POSIX_GUARD(s2n_stuffer_write_bytes(&base64_stuffer, (uint8_t *) &c, 1));
    };

    /* Flush any remaining bytes to asn1 */
    POSIX_GUARD(s2n_stuffer_read_base64(&base64_stuffer, asn1));

    return S2N_SUCCESS;
}

static int s2n_stuffer_data_from_pem(struct s2n_stuffer *pem, struct s2n_stuffer *asn1, const char *keyword)
{
    POSIX_PRECONDITION(s2n_stuffer_validate(pem));
    POSIX_PRECONDITION(s2n_stuffer_validate(asn1));
    POSIX_ENSURE_REF(keyword);

    POSIX_GUARD(s2n_stuffer_pem_read_begin(pem, keyword));
    POSIX_GUARD(s2n_stuffer_pem_read_contents(pem, asn1));
    POSIX_GUARD(s2n_stuffer_pem_read_end(pem, keyword));

    POSIX_POSTCONDITION(s2n_stuffer_validate(pem));
    POSIX_POSTCONDITION(s2n_stuffer_validate(asn1));
    return S2N_SUCCESS;
}

int s2n_stuffer_private_key_from_pem(struct s2n_stuffer *pem, struct s2n_stuffer *asn1, int *type)
{
    POSIX_PRECONDITION(s2n_stuffer_validate(pem));
    POSIX_PRECONDITION(s2n_stuffer_validate(asn1));
    POSIX_ENSURE_REF(type);

    if (s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_PKCS1_RSA_PRIVATE_KEY) == S2N_SUCCESS) {
        *type = EVP_PKEY_RSA;
        return S2N_SUCCESS;
    }

    POSIX_GUARD(s2n_stuffer_reread(pem));
    POSIX_GUARD(s2n_stuffer_reread(asn1));

    /* By default, OpenSSL tools always generate both "EC PARAMETERS" and "EC PRIVATE
     * KEY" PEM objects in the keyfile. Skip the first "EC PARAMETERS" object so that we're
     * compatible with OpenSSL's default output, and since "EC PARAMETERS" is
     * only needed for non-standard curves that aren't currently supported.
     */
    if (s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_EC_PARAMETERS) != S2N_SUCCESS) {
        POSIX_GUARD(s2n_stuffer_reread(pem));
    }
    POSIX_GUARD(s2n_stuffer_wipe(asn1));

    if (s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_PKCS1_EC_PRIVATE_KEY) == S2N_SUCCESS) {
        *type = EVP_PKEY_EC;
        return S2N_SUCCESS;
    }

    /* If it does not match either format, try PKCS#8 */
    POSIX_GUARD(s2n_stuffer_reread(pem));
    POSIX_GUARD(s2n_stuffer_reread(asn1));
    if (s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_PKCS8_PRIVATE_KEY) == S2N_SUCCESS) {
        *type = EVP_PKEY_RSA;
        return S2N_SUCCESS;
    }

    POSIX_BAIL(S2N_ERR_INVALID_PEM);
}

/* We define a pem containing a certificate as a pem containing the delimiter chars.
 * If the delimiter chars exist but the certificate keyword doesn't, that is a parsing error.
 * That ensures that we don't ignore unexpected keywords like "END CERTIFICATE"
 * instead of "BEGIN CERTIFICATE" or malformed keywords like "BEGAN CERTIFICATE"
 * instead of "BEGIN CERTIFICATE".
 */
bool s2n_stuffer_pem_has_certificate(struct s2n_stuffer *pem)
{
    /* Operate on a copy of pem to avoid modifying pem */
    struct s2n_stuffer pem_copy = *pem;
    return s2n_result_is_ok(s2n_stuffer_pem_read_delimiter_chars(&pem_copy));
}

int s2n_stuffer_certificate_from_pem(struct s2n_stuffer *pem, struct s2n_stuffer *asn1)
{
    return s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_CERTIFICATE);
}

int s2n_stuffer_crl_from_pem(struct s2n_stuffer *pem, struct s2n_stuffer *asn1)
{
    return s2n_stuffer_data_from_pem(pem, asn1, S2N_PEM_CRL);
}

int s2n_stuffer_dhparams_from_pem(struct s2n_stuffer *pem, struct s2n_stuffer *pkcs3)
{
    return s2n_stuffer_data_from_pem(pem, pkcs3, S2N_PEM_DH_PARAMETERS);
}