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Improve and document low-level PEM read routines

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PEM_read(), PEM_read_bio(), PEM_get_EVP_CIPHER_INFO() and
PEM_do_header().

Reviewed-by: Dr. Stephen Henson <steve@openssl.org>
This commit is contained in:
Viktor Dukhovni 2016-04-24 19:48:50 -04:00
parent 276fa9bda9
commit 67787844f1
2 changed files with 197 additions and 68 deletions
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175
crypto/pem/pem_lib.c
View file

@ -9,6 +9,7 @@
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include "internal/cryptlib.h"
#include <openssl/buffer.h>
#include <openssl/objects.h>
@ -389,115 +390,153 @@ int PEM_ASN1_write_bio(i2d_of_void *i2d, const char *name, BIO *bp,
int PEM_do_header(EVP_CIPHER_INFO *cipher, unsigned char *data, long *plen,
pem_password_cb *callback, void *u)
{
int i = 0, j, o, klen;
long len;
int ok;
int keylen;
long len = *plen;
int ilen = (int) len; /* EVP_DecryptUpdate etc. take int lengths */
EVP_CIPHER_CTX *ctx;
unsigned char key[EVP_MAX_KEY_LENGTH];
char buf[PEM_BUFSIZE];
len = *plen;
#if LONG_MAX > INT_MAX
/* Check that we did not truncate the length */
if (len > INT_MAX) {
PEMerr(PEM_F_PEM_DO_HEADER, PEM_R_HEADER_TOO_LONG);
return 0;
}
#endif
if (cipher->cipher == NULL)
return (1);
return 1;
if (callback == NULL)
klen = PEM_def_callback(buf, PEM_BUFSIZE, 0, u);
keylen = PEM_def_callback(buf, PEM_BUFSIZE, 0, u);
else
klen = callback(buf, PEM_BUFSIZE, 0, u);
if (klen <= 0) {
keylen = callback(buf, PEM_BUFSIZE, 0, u);
if (keylen <= 0) {
PEMerr(PEM_F_PEM_DO_HEADER, PEM_R_BAD_PASSWORD_READ);
return (0);
return 0;
}
#ifdef CHARSET_EBCDIC
/* Convert the pass phrase from EBCDIC */
ebcdic2ascii(buf, buf, klen);
ebcdic2ascii(buf, buf, keylen);
#endif
if (!EVP_BytesToKey(cipher->cipher, EVP_md5(), &(cipher->iv[0]),
(unsigned char *)buf, klen, 1, key, NULL))
(unsigned char *)buf, keylen, 1, key, NULL))
return 0;
j = (int)len;
ctx = EVP_CIPHER_CTX_new();
if (ctx == NULL)
return 0;
o = EVP_DecryptInit_ex(ctx, cipher->cipher, NULL, key, &(cipher->iv[0]));
if (o)
o = EVP_DecryptUpdate(ctx, data, &i, data, j);
if (o)
o = EVP_DecryptFinal_ex(ctx, &(data[i]), &j);
ok = EVP_DecryptInit_ex(ctx, cipher->cipher, NULL, key, &(cipher->iv[0]));
if (ok)
ok = EVP_DecryptUpdate(ctx, data, &ilen, data, ilen);
if (ok) {
/* Squirrel away the length of data decrypted so far. */
*plen = ilen;
ok = EVP_DecryptFinal_ex(ctx, &(data[ilen]), &ilen);
}
if (ok)
*plen += ilen;
else
PEMerr(PEM_F_PEM_DO_HEADER, PEM_R_BAD_DECRYPT);
EVP_CIPHER_CTX_free(ctx);
OPENSSL_cleanse((char *)buf, sizeof(buf));
OPENSSL_cleanse((char *)key, sizeof(key));
if (o)
j += i;
else {
PEMerr(PEM_F_PEM_DO_HEADER, PEM_R_BAD_DECRYPT);
return (0);
}
*plen = j;
return (1);
return ok;
}
/*
* This implements a very limited PEM header parser that does not support the
* full grammar of rfc1421. In particular, folded headers are not supported,
* nor is additional whitespace.
*
* A robust implementation would make use of a library that turns the headers
* into a BIO from which one folded line is read at a time, and is then split
* into a header label and content. We would then parse the content of the
* headers we care about. This is overkill for just this limited use-case, but
* presumably we also parse rfc822-style headers for S/MIME, so a common
* abstraction might well be more generally useful.
*/
int PEM_get_EVP_CIPHER_INFO(char *header, EVP_CIPHER_INFO *cipher)
{
static const char ProcType[] = "Proc-Type:";
static const char ENCRYPTED[] = "ENCRYPTED";
static const char DEKInfo[] = "DEK-Info:";
const EVP_CIPHER *enc = NULL;
int ivlen;
char *dekinfostart, c;
cipher->cipher = NULL;
if ((header == NULL) || (*header == '\0') || (*header == '\n'))
return (1);
if (strncmp(header, "Proc-Type: ", 11) != 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_PROC_TYPE);
return (0);
}
header += 11;
if (*header != '4')
return (0);
header++;
if (*header != ',')
return (0);
header++;
if (strncmp(header, "ENCRYPTED", 9) != 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_ENCRYPTED);
return (0);
}
for (; (*header != '\n') && (*header != '\0'); header++) ;
if (*header == '\0') {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_SHORT_HEADER);
return (0);
}
header++;
if (strncmp(header, "DEK-Info: ", 10) != 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_DEK_INFO);
return (0);
}
header += 10;
return 1;
dekinfostart = header;
for (;;) {
c = *header;
#ifndef CHARSET_EBCDIC
if (!(((c >= 'A') && (c <= 'Z')) || (c == '-') ||
((c >= '0') && (c <= '9'))))
break;
#else
if (!(isupper(c) || (c == '-') || isdigit(c)))
break;
#endif
header++;
if (strncmp(header, ProcType, sizeof(ProcType)-1) != 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_PROC_TYPE);
return 0;
}
header += sizeof(ProcType)-1;
header += strspn(header, " \t");
if (*header++ != '4' || *header++ != ',')
return 0;
header += strspn(header, " \t");
/* We expect "ENCRYPTED" followed by optional white-space + line break */
if (strncmp(header, ENCRYPTED, sizeof(ENCRYPTED)-1) != 0 ||
strspn(header+sizeof(ENCRYPTED)-1, " \t\r\n") == 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_ENCRYPTED);
return 0;
}
header += sizeof(ENCRYPTED)-1;
header += strspn(header, " \t\r");
if (*header++ != '\n') {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_SHORT_HEADER);
return 0;
}
/*-
* https://tools.ietf.org/html/rfc1421#section-4.6.1.3
* We expect "DEK-Info: algo[,hex-parameters]"
*/
if (strncmp(header, DEKInfo, sizeof(DEKInfo)-1) != 0) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_NOT_DEK_INFO);
return 0;
}
header += sizeof(DEKInfo)-1;
header += strspn(header, " \t");
/*
* DEK-INFO is a comma-separated combination of algorithm name and optional
* parameters.
*/
dekinfostart = header;
header += strcspn(header, " \t,");
c = *header;
*header = '\0';
cipher->cipher = enc = EVP_get_cipherbyname(dekinfostart);
*header++ = c;
*header = c;
header += strspn(header, " \t");
if (enc == NULL) {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_UNSUPPORTED_ENCRYPTION);
return (0);
return 0;
}
ivlen = EVP_CIPHER_iv_length(enc);
if (ivlen > 0 && *header++ != ',') {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_MISSING_DEK_IV);
return 0;
} else if (ivlen == 0 && *header == ',') {
PEMerr(PEM_F_PEM_GET_EVP_CIPHER_INFO, PEM_R_UNEXPECTED_DEK_IV);
return 0;
}
if (!load_iv(&header, cipher->iv, EVP_CIPHER_iv_length(enc)))
return (0);
return (1);
if (!load_iv(&header, cipher->iv, EVP_CIPHER_iv_length(enc)))
return 0;
return 1;
}
static int load_iv(char **fromp, unsigned char *to, int num)

90
doc/crypto/pem_read.pod Normal file
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@ -0,0 +1,90 @@
=pod
=head1 NAME
PEM_read, PEM_read_bio, PEM_do_header - low-level PEM routines
=head1 SYNOPSIS
#include <openssl/pem.h>
int PEM_read(FILE *fp, char **name, char **header,
unsigned char **data, long *len);
int PEM_read_bio(BIO *bp, char **name, char **header,
unsigned char **data, long *len);
int PEM_get_EVP_CIPHER_INFO(char *header, EVP_CIPHER_INFO *cinfo);
int PEM_do_header(EVP_CIPHER_INFO *cinfo, unsigned char *data, long *len,
pem_password_cb *cb, void *u);
=head1 DESCRIPTION
These functions read and decode PEM-encoded objects, returning the
PEM type B<name>, any encapsulation B<header> and the decoded
B<data> of length B<len>.
PEM_read() reads from the stdio file handle B<fp>, while PEM_read_bio() reads
from the BIO B<bio>.
Both skip any non-PEM data that precedes the start of the next PEM object.
When an object is successfuly retrieved, the type name from the "----BEGIN
<type>-----" is returned via the B<name> argument, any encapsulation headers
are returned in B<header> and the base64-decoded content and its length are
returned via B<data> and B<len> respectively.
The B<name>, B<header> and B<data> pointers are allocated via OPENSSL_malloc()
and should be freed by the caller via OPENSSL_free() when no longer needed.
PEM_get_EVP_CIPHER_INFO() can be used to determine the B<data> returned by
PEM_read() or PEM_read_bio() is encrypted and to retrieve the associated cipher
and IV.
The caller passes a pointer to structure of type B<EVP_CIPHER_INFO> via the
B<cinfo> argument and the B<header> returned via PEM_read() or PEM_read_bio().
If the call is succesful 1 is retured and the cipher and IV are stored at the
address pointed to by B<cinfo>.
When the header is malformed, or not supported or when the cipher is unknown
or some internal error happens 0 is returned.
This function is deprecated, see B<NOTES> below.
PEM_do_header() can then be used to decrypt the data if the header
indicates encryption.
The B<cinfo> argument is a pointer to the structure initialized by the previous
call to PEM_get_EVP_CIPHER_INFO().
The B<data> and B<len> arguments are those returned by the previous call to
PEM_read() or PEM_read_bio().
The B<cb> and B<u> arguments make it possible to override the default password
prompt function as described in L<pem(3)>.
On successful completion the B<data> is decrypted in place, and B<len> is
updated to indicate the plaintext length.
This function is deprecated, see B<NOTES> below.
If the data is a priori known to not be encrypted, then neither PEM_do_header()
nor PEM_get_EVP_CIPHER_INFO() need be called.
The final B<data> buffer is typically an ASN.1 object which can be decoded with
the B<d2i> function appropriate to the type B<name>.
=head1 RETURN VALUES
PEM_read() and PEM_read_bio() return 1 on success and 0 on failure, the latter
includes the case when no more PEM objects remain in the input file.
To distinguish end of file from more serious errors the caller must peek at the
error stack and check for B<PEM_R_NO_START_LINE>, which indicates that no more
PEM objects were found. See L<ERR_peek_last_error(3)>, L<ERR_GET_REASON(3)>.
PEM_get_EVP_CIPHER_INFO() and PEM_do_header() return 1 on success, and 0 on
failure.
The B<data> is likely meaningless if these functions fail.
=head1 NOTES
The PEM_get_EVP_CIPHER_INFO() and PEM_do_header() functions are deprecated.
This is because the underlying PEM encryption format is obsolete, and should
be avoided.
It uses an encryption format with an OpenSSL-specific key-derivation function,
which employs MD5 with an iteration count of 1!
Instead, private keys should be stored in PKCS#8 form, with a strong PKCS#5
v2.0 PBE.
See L<pkcs8(1)> and L<pem(3)> and L<d2i_PKCS8PrivateKey_bio(3)>.
=head1 SEE ALSO
L<pem(3)>, L<ERR_peek_last_error(3)>, L<ERR_GET_LIB(3)>, L<pkcs8(1)>,
L<d2i_PKCS8PrivateKey_bio(3)>.