backports: add signature verification code

Uh, this was awful. Because the crypto/ things are completely
impossible to backport, I've actually implemented this by using
mbedtls and embedding the relevant functions it has...

The mbedtls code is taken from mbedtls version 2.6.0 and only
minimally modified (mostly to remove <string.h> and similar).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 618 insertions, 0 deletions

diff --git a/backport/compat/verification/mbedtls/pk.h b/backport/compat/verification/mbedtls/pk.h
new file mode 100644
index 00000000..9aac7e2a
--- /dev/null
+++ b/backport/compat/verification/mbedtls/pk.h
@@ -0,0 +1,618 @@
+/**
+ * \file pk.h
+ *
+ * \brief Public Key abstraction layer
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: GPL-2.0
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+#ifndef MBEDTLS_PK_H
+#define MBEDTLS_PK_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include "md.h"
+
+#if defined(MBEDTLS_RSA_C)
+#include "rsa.h"
+#endif
+
+#if defined(MBEDTLS_ECP_C)
+#include "ecp.h"
+#endif
+
+#if defined(MBEDTLS_ECDSA_C)
+#include "ecdsa.h"
+#endif
+
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
+    !defined(inline) && !defined(__cplusplus)
+#define inline __inline
+#endif
+
+#define MBEDTLS_ERR_PK_ALLOC_FAILED        -0x3F80  /**< Memory allocation failed. */
+#define MBEDTLS_ERR_PK_TYPE_MISMATCH       -0x3F00  /**< Type mismatch, eg attempt to encrypt with an ECDSA key */
+#define MBEDTLS_ERR_PK_BAD_INPUT_DATA      -0x3E80  /**< Bad input parameters to function. */
+#define MBEDTLS_ERR_PK_FILE_IO_ERROR       -0x3E00  /**< Read/write of file failed. */
+#define MBEDTLS_ERR_PK_KEY_INVALID_VERSION -0x3D80  /**< Unsupported key version */
+#define MBEDTLS_ERR_PK_KEY_INVALID_FORMAT  -0x3D00  /**< Invalid key tag or value. */
+#define MBEDTLS_ERR_PK_UNKNOWN_PK_ALG      -0x3C80  /**< Key algorithm is unsupported (only RSA and EC are supported). */
+#define MBEDTLS_ERR_PK_PASSWORD_REQUIRED   -0x3C00  /**< Private key password can't be empty. */
+#define MBEDTLS_ERR_PK_PASSWORD_MISMATCH   -0x3B80  /**< Given private key password does not allow for correct decryption. */
+#define MBEDTLS_ERR_PK_INVALID_PUBKEY      -0x3B00  /**< The pubkey tag or value is invalid (only RSA and EC are supported). */
+#define MBEDTLS_ERR_PK_INVALID_ALG         -0x3A80  /**< The algorithm tag or value is invalid. */
+#define MBEDTLS_ERR_PK_UNKNOWN_NAMED_CURVE -0x3A00  /**< Elliptic curve is unsupported (only NIST curves are supported). */
+#define MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE -0x3980  /**< Unavailable feature, e.g. RSA disabled for RSA key. */
+#define MBEDTLS_ERR_PK_SIG_LEN_MISMATCH    -0x3900  /**< The signature is valid but its length is less than expected. */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \brief          Public key types
+ */
+typedef enum {
+    MBEDTLS_PK_NONE=0,
+    MBEDTLS_PK_RSA,
+    MBEDTLS_PK_ECKEY,
+    MBEDTLS_PK_ECKEY_DH,
+    MBEDTLS_PK_ECDSA,
+    MBEDTLS_PK_RSA_ALT,
+    MBEDTLS_PK_RSASSA_PSS,
+} mbedtls_pk_type_t;
+
+/**
+ * \brief           Options for RSASSA-PSS signature verification.
+ *                  See \c mbedtls_rsa_rsassa_pss_verify_ext()
+ */
+typedef struct
+{
+    mbedtls_md_type_t mgf1_hash_id;
+    int expected_salt_len;
+
+} mbedtls_pk_rsassa_pss_options;
+
+/**
+ * \brief           Types for interfacing with the debug module
+ */
+typedef enum
+{
+    MBEDTLS_PK_DEBUG_NONE = 0,
+    MBEDTLS_PK_DEBUG_MPI,
+    MBEDTLS_PK_DEBUG_ECP,
+} mbedtls_pk_debug_type;
+
+/**
+ * \brief           Item to send to the debug module
+ */
+typedef struct
+{
+    mbedtls_pk_debug_type type;
+    const char *name;
+    void *value;
+} mbedtls_pk_debug_item;
+
+/** Maximum number of item send for debugging, plus 1 */
+#define MBEDTLS_PK_DEBUG_MAX_ITEMS 3
+
+/**
+ * \brief           Public key information and operations
+ */
+typedef struct mbedtls_pk_info_t mbedtls_pk_info_t;
+
+/**
+ * \brief           Public key container
+ */
+typedef struct
+{
+    const mbedtls_pk_info_t *   pk_info; /**< Public key informations        */
+    void *                      pk_ctx;  /**< Underlying public key context  */
+} mbedtls_pk_context;
+
+#if defined(MBEDTLS_RSA_C)
+/**
+ * Quick access to an RSA context inside a PK context.
+ *
+ * \warning You must make sure the PK context actually holds an RSA context
+ * before using this function!
+ */
+static inline mbedtls_rsa_context *mbedtls_pk_rsa( const mbedtls_pk_context pk )
+{
+    return( (mbedtls_rsa_context *) (pk).pk_ctx );
+}
+#endif /* MBEDTLS_RSA_C */
+
+#if defined(MBEDTLS_ECP_C)
+/**
+ * Quick access to an EC context inside a PK context.
+ *
+ * \warning You must make sure the PK context actually holds an EC context
+ * before using this function!
+ */
+static inline mbedtls_ecp_keypair *mbedtls_pk_ec( const mbedtls_pk_context pk )
+{
+    return( (mbedtls_ecp_keypair *) (pk).pk_ctx );
+}
+#endif /* MBEDTLS_ECP_C */
+
+#if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
+/**
+ * \brief           Types for RSA-alt abstraction
+ */
+typedef int (*mbedtls_pk_rsa_alt_decrypt_func)( void *ctx, int mode, size_t *olen,
+                    const unsigned char *input, unsigned char *output,
+                    size_t output_max_len );
+typedef int (*mbedtls_pk_rsa_alt_sign_func)( void *ctx,
+                    int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
+                    int mode, mbedtls_md_type_t md_alg, unsigned int hashlen,
+                    const unsigned char *hash, unsigned char *sig );
+typedef size_t (*mbedtls_pk_rsa_alt_key_len_func)( void *ctx );
+#endif /* MBEDTLS_PK_RSA_ALT_SUPPORT */
+
+/**
+ * \brief           Return information associated with the given PK type
+ *
+ * \param pk_type   PK type to search for.
+ *
+ * \return          The PK info associated with the type or NULL if not found.
+ */
+const mbedtls_pk_info_t *mbedtls_pk_info_from_type( mbedtls_pk_type_t pk_type );
+
+/**
+ * \brief           Initialize a mbedtls_pk_context (as NONE)
+ */
+void mbedtls_pk_init( mbedtls_pk_context *ctx );
+
+/**
+ * \brief           Free a mbedtls_pk_context
+ */
+void mbedtls_pk_free( mbedtls_pk_context *ctx );
+
+/**
+ * \brief           Initialize a PK context with the information given
+ *                  and allocates the type-specific PK subcontext.
+ *
+ * \param ctx       Context to initialize. Must be empty (type NONE).
+ * \param info      Information to use
+ *
+ * \return          0 on success,
+ *                  MBEDTLS_ERR_PK_BAD_INPUT_DATA on invalid input,
+ *                  MBEDTLS_ERR_PK_ALLOC_FAILED on allocation failure.
+ *
+ * \note            For contexts holding an RSA-alt key, use
+ *                  \c mbedtls_pk_setup_rsa_alt() instead.
+ */
+int mbedtls_pk_setup( mbedtls_pk_context *ctx, const mbedtls_pk_info_t *info );
+
+#if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
+/**
+ * \brief           Initialize an RSA-alt context
+ *
+ * \param ctx       Context to initialize. Must be empty (type NONE).
+ * \param key       RSA key pointer
+ * \param decrypt_func  Decryption function
+ * \param sign_func     Signing function
+ * \param key_len_func  Function returning key length in bytes
+ *
+ * \return          0 on success, or MBEDTLS_ERR_PK_BAD_INPUT_DATA if the
+ *                  context wasn't already initialized as RSA_ALT.
+ *
+ * \note            This function replaces \c mbedtls_pk_setup() for RSA-alt.
+ */
+int mbedtls_pk_setup_rsa_alt( mbedtls_pk_context *ctx, void * key,
+                         mbedtls_pk_rsa_alt_decrypt_func decrypt_func,
+                         mbedtls_pk_rsa_alt_sign_func sign_func,
+                         mbedtls_pk_rsa_alt_key_len_func key_len_func );
+#endif /* MBEDTLS_PK_RSA_ALT_SUPPORT */
+
+/**
+ * \brief           Get the size in bits of the underlying key
+ *
+ * \param ctx       Context to use
+ *
+ * \return          Key size in bits, or 0 on error
+ */
+size_t mbedtls_pk_get_bitlen( const mbedtls_pk_context *ctx );
+
+/**
+ * \brief           Get the length in bytes of the underlying key
+ * \param ctx       Context to use
+ *
+ * \return          Key length in bytes, or 0 on error
+ */
+static inline size_t mbedtls_pk_get_len( const mbedtls_pk_context *ctx )
+{
+    return( ( mbedtls_pk_get_bitlen( ctx ) + 7 ) / 8 );
+}
+
+/**
+ * \brief           Tell if a context can do the operation given by type
+ *
+ * \param ctx       Context to test
+ * \param type      Target type
+ *
+ * \return          0 if context can't do the operations,
+ *                  1 otherwise.
+ */
+int mbedtls_pk_can_do( const mbedtls_pk_context *ctx, mbedtls_pk_type_t type );
+
+/**
+ * \brief           Verify signature (including padding if relevant).
+ *
+ * \param ctx       PK context to use
+ * \param md_alg    Hash algorithm used (see notes)
+ * \param hash      Hash of the message to sign
+ * \param hash_len  Hash length or 0 (see notes)
+ * \param sig       Signature to verify
+ * \param sig_len   Signature length
+ *
+ * \return          0 on success (signature is valid),
+ *                  MBEDTLS_ERR_PK_SIG_LEN_MISMATCH if the signature is
+ *                  valid but its actual length is less than sig_len,
+ *                  or a specific error code.
+ *
+ * \note            For RSA keys, the default padding type is PKCS#1 v1.5.
+ *                  Use \c mbedtls_pk_verify_ext( MBEDTLS_PK_RSASSA_PSS, ... )
+ *                  to verify RSASSA_PSS signatures.
+ *
+ * \note            If hash_len is 0, then the length associated with md_alg
+ *                  is used instead, or an error returned if it is invalid.
+ *
+ * \note            md_alg may be MBEDTLS_MD_NONE, only if hash_len != 0
+ */
+int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+               const unsigned char *hash, size_t hash_len,
+               const unsigned char *sig, size_t sig_len );
+
+/**
+ * \brief           Verify signature, with options.
+ *                  (Includes verification of the padding depending on type.)
+ *
+ * \param type      Signature type (inc. possible padding type) to verify
+ * \param options   Pointer to type-specific options, or NULL
+ * \param ctx       PK context to use
+ * \param md_alg    Hash algorithm used (see notes)
+ * \param hash      Hash of the message to sign
+ * \param hash_len  Hash length or 0 (see notes)
+ * \param sig       Signature to verify
+ * \param sig_len   Signature length
+ *
+ * \return          0 on success (signature is valid),
+ *                  MBEDTLS_ERR_PK_TYPE_MISMATCH if the PK context can't be
+ *                  used for this type of signatures,
+ *                  MBEDTLS_ERR_PK_SIG_LEN_MISMATCH if the signature is
+ *                  valid but its actual length is less than sig_len,
+ *                  or a specific error code.
+ *
+ * \note            If hash_len is 0, then the length associated with md_alg
+ *                  is used instead, or an error returned if it is invalid.
+ *
+ * \note            md_alg may be MBEDTLS_MD_NONE, only if hash_len != 0
+ *
+ * \note            If type is MBEDTLS_PK_RSASSA_PSS, then options must point
+ *                  to a mbedtls_pk_rsassa_pss_options structure,
+ *                  otherwise it must be NULL.
+ */
+int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
+                   mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+                   const unsigned char *hash, size_t hash_len,
+                   const unsigned char *sig, size_t sig_len );
+
+/**
+ * \brief           Make signature, including padding if relevant.
+ *
+ * \param ctx       PK context to use - must hold a private key
+ * \param md_alg    Hash algorithm used (see notes)
+ * \param hash      Hash of the message to sign
+ * \param hash_len  Hash length or 0 (see notes)
+ * \param sig       Place to write the signature
+ * \param sig_len   Number of bytes written
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ *
+ * \return          0 on success, or a specific error code.
+ *
+ * \note            For RSA keys, the default padding type is PKCS#1 v1.5.
+ *                  There is no interface in the PK module to make RSASSA-PSS
+ *                  signatures yet.
+ *
+ * \note            If hash_len is 0, then the length associated with md_alg
+ *                  is used instead, or an error returned if it is invalid.
+ *
+ * \note            For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
+ *                  For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
+ */
+int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+             const unsigned char *hash, size_t hash_len,
+             unsigned char *sig, size_t *sig_len,
+             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
+
+/**
+ * \brief           Decrypt message (including padding if relevant).
+ *
+ * \param ctx       PK context to use - must hold a private key
+ * \param input     Input to decrypt
+ * \param ilen      Input size
+ * \param output    Decrypted output
+ * \param olen      Decrypted message length
+ * \param osize     Size of the output buffer
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ *
+ * \note            For RSA keys, the default padding type is PKCS#1 v1.5.
+ *
+ * \return          0 on success, or a specific error code.
+ */
+int mbedtls_pk_decrypt( mbedtls_pk_context *ctx,
+                const unsigned char *input, size_t ilen,
+                unsigned char *output, size_t *olen, size_t osize,
+                int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
+
+/**
+ * \brief           Encrypt message (including padding if relevant).
+ *
+ * \param ctx       PK context to use
+ * \param input     Message to encrypt
+ * \param ilen      Message size
+ * \param output    Encrypted output
+ * \param olen      Encrypted output length
+ * \param osize     Size of the output buffer
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ *
+ * \note            For RSA keys, the default padding type is PKCS#1 v1.5.
+ *
+ * \return          0 on success, or a specific error code.
+ */
+int mbedtls_pk_encrypt( mbedtls_pk_context *ctx,
+                const unsigned char *input, size_t ilen,
+                unsigned char *output, size_t *olen, size_t osize,
+                int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
+
+/**
+ * \brief           Check if a public-private pair of keys matches.
+ *
+ * \param pub       Context holding a public key.
+ * \param prv       Context holding a private (and public) key.
+ *
+ * \return          0 on success or MBEDTLS_ERR_PK_BAD_INPUT_DATA
+ */
+int mbedtls_pk_check_pair( const mbedtls_pk_context *pub, const mbedtls_pk_context *prv );
+
+/**
+ * \brief           Export debug information
+ *
+ * \param ctx       Context to use
+ * \param items     Place to write debug items
+ *
+ * \return          0 on success or MBEDTLS_ERR_PK_BAD_INPUT_DATA
+ */
+int mbedtls_pk_debug( const mbedtls_pk_context *ctx, mbedtls_pk_debug_item *items );
+
+/**
+ * \brief           Access the type name
+ *
+ * \param ctx       Context to use
+ *
+ * \return          Type name on success, or "invalid PK"
+ */
+const char * mbedtls_pk_get_name( const mbedtls_pk_context *ctx );
+
+/**
+ * \brief           Get the key type
+ *
+ * \param ctx       Context to use
+ *
+ * \return          Type on success, or MBEDTLS_PK_NONE
+ */
+mbedtls_pk_type_t mbedtls_pk_get_type( const mbedtls_pk_context *ctx );
+
+#if defined(MBEDTLS_PK_PARSE_C)
+/** \ingroup pk_module */
+/**
+ * \brief           Parse a private key in PEM or DER format
+ *
+ * \param ctx       key to be initialized
+ * \param key       input buffer
+ * \param keylen    size of the buffer
+ *                  (including the terminating null byte for PEM data)
+ * \param pwd       password for decryption (optional)
+ * \param pwdlen    size of the password
+ *
+ * \note            On entry, ctx must be empty, either freshly initialised
+ *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
+ *                  specific key type, check the result with mbedtls_pk_can_do().
+ *
+ * \note            The key is also checked for correctness.
+ *
+ * \return          0 if successful, or a specific PK or PEM error code
+ */
+int mbedtls_pk_parse_key( mbedtls_pk_context *ctx,
+                  const unsigned char *key, size_t keylen,
+                  const unsigned char *pwd, size_t pwdlen );
+
+/** \ingroup pk_module */
+/**
+ * \brief           Parse a public key in PEM or DER format
+ *
+ * \param ctx       key to be initialized
+ * \param key       input buffer
+ * \param keylen    size of the buffer
+ *                  (including the terminating null byte for PEM data)
+ *
+ * \note            On entry, ctx must be empty, either freshly initialised
+ *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
+ *                  specific key type, check the result with mbedtls_pk_can_do().
+ *
+ * \note            The key is also checked for correctness.
+ *
+ * \return          0 if successful, or a specific PK or PEM error code
+ */
+int mbedtls_pk_parse_public_key( mbedtls_pk_context *ctx,
+                         const unsigned char *key, size_t keylen );
+
+#if defined(MBEDTLS_FS_IO)
+/** \ingroup pk_module */
+/**
+ * \brief           Load and parse a private key
+ *
+ * \param ctx       key to be initialized
+ * \param path      filename to read the private key from
+ * \param password  password to decrypt the file (can be NULL)
+ *
+ * \note            On entry, ctx must be empty, either freshly initialised
+ *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
+ *                  specific key type, check the result with mbedtls_pk_can_do().
+ *
+ * \note            The key is also checked for correctness.
+ *
+ * \return          0 if successful, or a specific PK or PEM error code
+ */
+int mbedtls_pk_parse_keyfile( mbedtls_pk_context *ctx,
+                      const char *path, const char *password );
+
+/** \ingroup pk_module */
+/**
+ * \brief           Load and parse a public key
+ *
+ * \param ctx       key to be initialized
+ * \param path      filename to read the public key from
+ *
+ * \note            On entry, ctx must be empty, either freshly initialised
+ *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If
+ *                  you need a specific key type, check the result with
+ *                  mbedtls_pk_can_do().
+ *
+ * \note            The key is also checked for correctness.
+ *
+ * \return          0 if successful, or a specific PK or PEM error code
+ */
+int mbedtls_pk_parse_public_keyfile( mbedtls_pk_context *ctx, const char *path );
+#endif /* MBEDTLS_FS_IO */
+#endif /* MBEDTLS_PK_PARSE_C */
+
+#if defined(MBEDTLS_PK_WRITE_C)
+/**
+ * \brief           Write a private key to a PKCS#1 or SEC1 DER structure
+ *                  Note: data is written at the end of the buffer! Use the
+ *                        return value to determine where you should start
+ *                        using the buffer
+ *
+ * \param ctx       private to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ *
+ * \return          length of data written if successful, or a specific
+ *                  error code
+ */
+int mbedtls_pk_write_key_der( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+
+/**
+ * \brief           Write a public key to a SubjectPublicKeyInfo DER structure
+ *                  Note: data is written at the end of the buffer! Use the
+ *                        return value to determine where you should start
+ *                        using the buffer
+ *
+ * \param ctx       public key to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ *
+ * \return          length of data written if successful, or a specific
+ *                  error code
+ */
+int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+
+#if defined(MBEDTLS_PEM_WRITE_C)
+/**
+ * \brief           Write a public key to a PEM string
+ *
+ * \param ctx       public key to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ *
+ * \return          0 if successful, or a specific error code
+ */
+int mbedtls_pk_write_pubkey_pem( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+
+/**
+ * \brief           Write a private key to a PKCS#1 or SEC1 PEM string
+ *
+ * \param ctx       private to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ *
+ * \return          0 if successful, or a specific error code
+ */
+int mbedtls_pk_write_key_pem( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+#endif /* MBEDTLS_PEM_WRITE_C */
+#endif /* MBEDTLS_PK_WRITE_C */
+
+/*
+ * WARNING: Low-level functions. You probably do not want to use these unless
+ *          you are certain you do ;)
+ */
+
+#if defined(MBEDTLS_PK_PARSE_C)
+/**
+ * \brief           Parse a SubjectPublicKeyInfo DER structure
+ *
+ * \param p         the position in the ASN.1 data
+ * \param end       end of the buffer
+ * \param pk        the key to fill
+ *
+ * \return          0 if successful, or a specific PK error code
+ */
+int mbedtls_pk_parse_subpubkey( unsigned char **p, const unsigned char *end,
+                        mbedtls_pk_context *pk );
+#endif /* MBEDTLS_PK_PARSE_C */
+
+#if defined(MBEDTLS_PK_WRITE_C)
+/**
+ * \brief           Write a subjectPublicKey to ASN.1 data
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param key       public key to write away
+ *
+ * \return          the length written or a negative error code
+ */
+int mbedtls_pk_write_pubkey( unsigned char **p, unsigned char *start,
+                     const mbedtls_pk_context *key );
+#endif /* MBEDTLS_PK_WRITE_C */
+
+/*
+ * Internal module functions. You probably do not want to use these unless you
+ * know you do.
+ */
+#if defined(MBEDTLS_FS_IO)
+int mbedtls_pk_load_file( const char *path, unsigned char **buf, size_t *n );
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MBEDTLS_PK_H */