OpenSSL BIO Series 23 --- MD type Bio

MD type BIO

--- Translation according to OpenSSL DOC / CRYPTO / BIO_F_MD.POD and its own understanding

(Author: DragonKing, Mail: wzhah@263.net, Posted on: http: //gdwzh.126.com of openssl professional forum)

This type is filter type BIO, which is defined as follows (OpenSSL / BIO.H, OpenSSL / EVP.H):

BIO_METHOD * BIO_F_MD (VOID);

INT BIO_SET_MD (BIO * B, EVP_MD * MD);

INT BIO_GET_MD (BIO * B, EVP_MD ** MDP);

INT BIO_GET_MD_CTX (BIO * B, EVP_MD_CTX ** MDCP);

As with the Cipher type, some definitions and implementations of this type are in EVP / BIO_MD.C instead of in the Bio directory. If you want to see the source file, please refer to this file.

[BIO_F_MD]

This function returns a MD type BIO_METHOD structure, which is defined as follows:

Static Bio_Method Methods_md =

{

BIO_TYPE_MD, "Message Digest",

MD_WRITE,

MD_READ,

NULL, / * MD_PUTS, * /

MD_GETS,

Md_ctrl,

MD_NEW,

Md_free,

Md_callback_ctrl,

}

MD type BIO performs a summary operation over any of its data, in fact, the type BIO encapsulates the functions and behaviors of EVP_DIGESTINIT, EVP_DIGESTUPDATE and EVP_DigestFinal three functions. This type of BIO is completely symmetrical, that is, no matter whether it is reading data (BIO_READ) or writing data (Bio_WRITE), the same summary operation is performed.

When the BIO_GETS function is executed, if a given Size parameter is large enough, you can complete the summary calculation, then the summary value will be returned. The BIO_PUTS function is not supported. If this function needs to be supported, you can add a BUFFER type Bio in front.

The BIO_RESET function re-initializes a summary type Bio, in fact, it is simple to call the EVP_Digestinit function for initialization.

Note that after reading the summary information from a summary BIO, the BIO_RESET or BIO_SET_MD must be called before re-use the BIO.

[BIO_SET_MD]

This function is a macro definition function of a BIO_CTRL function that uses parameter MD to set a summary algorithm for a given BIO. This function must be called before performing the read and write operation, used to initialize a summary type of BIO. The call successfully returns 1, otherwise it returns 0.

[BIO_GET_MD]

This function is also a macro definition of the BIO_CTRL function. It returns the pointer to the BIO summary method to the MDP parameter. The call successfully returns 1, otherwise it returns 0.

[BIO_GET_MD_CTX]

This function returns the method structure of the summary BIO to the MDCP parameter. This structure can be used as a parameter in the EVP_DIGESTFINAL, EVP_SIGNFINAL and EVP_VERIFINAL functions, which adds flexibility. Since the structure returned by the function is a structure inside a BIO, any change operation of the structure affects the corresponding BIO, and if the BIO is released, the structural pointer is invalid. The call successfully returns 1, otherwise it returns 0.

[Examples] 1. The following examples create a Bio chain containing the SHA1 and MD5 Type Summary BIO, and performs data "Hello World" through them.

BIO * BIO, * MDTMP;

Char message [] = "Hello World";

BIO = BIO_NEW (BIO_S_NULL ());

MDTMP = BIO_NEW (BIO_F_MD ());

BIO_SET_MD (MDTMP, EVP_SHA1 ());

// Use Bio_Push to add a Sink type Bio in front of the BIO chain, as a flag started as a Bio chain

BIO = BIO_PUSH (MDTMP, BIO);

MDTMP = BIO_NEW (BIO_F_MD ());

BIO_SET_MD (MDTMP, EVP_MD5 ());

BIO = BIO_PUSH (MDTMP, BIO);

/ * Note that the MDTMP variable is now available * /

Bio_write (Bio, Message, Strlen (Message)); // Because the last Bio is a Null type Bio, the data is actually automatically discarded.

2. The following example demonstrates the process of reading data from a summary type BIO:

BIO * BIO, * MDTMP;

Char BUF [1024];

Int rdlen;

BIO = BIO_NEW_FILE (File, "RB");

MDTMP = BIO_NEW (BIO_F_MD ());

BIO_SET_MD (MDTMP, EVP_SHA1 ());

BIO = BIO_PUSH (MDTMP, BIO);

MDTMP = BIO_NEW (BIO_F_MD ());

BIO_SET_MD (MDTMP, EVP_MD5 ());

BIO = BIO_PUSH (MDTMP, BIO);

Do {

Rdlen = BIO_READ (Bio, BUF, SIZEOF (BUF));

/ * Can join the code of processing data in this * /

WHILE (RDLEN> 0);

3. The following example reads the summary data from a BIO chain and outputs. It can be used with the example above.

BIO * MDTMP;

Unsigned char mdbuf [evp_max_md_size];

Int mdlen;

INT I;

MDTMP = BIO; / * Here, the BIO has been set up * /

Do {

EVP_MD * MD;

MDTMP = BIO_FIND_TYPE (MDTMP, BIO_TYPE_MD);

IF (! MDTMP) Break;

BIO_GET_MD (MDTMP, & MD);

Printf ("% s DiGest", obj_nid2sn (eVP_md_type (md)));

MDLEN = BIO_GETS (MDTMP, MDBUF, EVP_MAX_MD_SIZE);

For (i = 0; I

Printf ("/ n");

MDTMP = BIO_NEXT (MDTMP);

WHILE (MDTMP);

BIO_FREE_ALL (BIO);