Openssl 从MD_CTX打印内容
我试图理解Openssl 从MD_CTX打印内容,openssl,printf,pass-by-reference,pass-by-value,message-digest,Openssl,Printf,Pass By Reference,Pass By Value,Message Digest,我试图理解md_rand.c中的哈希函数是如何工作的。假设我声明了一个变量MD\u CTX m,并且在每个MD\u Update函数之后,我试图查看m的内容 MD_Init(&m); printf("%X\n",*(&m)); MD_Update(&m,(unsigned char *)&(md_c[0]),sizeof(md_c)); printf("%X\n",*(&m)); MD_Update(&m,local_md,MD_DIGEST_LE
md_rand.c
中的哈希函数是如何工作的。假设我声明了一个变量MD\u CTX m
,并且在每个MD\u Update
函数之后,我试图查看m
的内容
MD_Init(&m);
printf("%X\n",*(&m));
MD_Update(&m,(unsigned char *)&(md_c[0]),sizeof(md_c));
printf("%X\n",*(&m));
MD_Update(&m,local_md,MD_DIGEST_LENGTH);
printf("%X\n",*(&m));
CRYPTO_w_lock(CRYPTO_LOCK_RAND);
MD_Update(&m,md,MD_DIGEST_LENGTH);
printf("%X\n",*(&m));
MD_Final(md,&m);
但是,每次MD\u更新之后,我总是为所有4个printf
语句打印出相同的值。我应该如何获得m
中的更新值
我应该怎么做才能得到m中的更新值
当您printf(“%X\n”、*(&m))
,您只是在堆栈上打印MD\u CTX
的地址。它永远不会改变,这就是你观察的原因
一个MD_CTX
是一个不透明的结构,这意味着你不应该查看它。它是一个typedef,您可以通过以下方式找到它:
$ cd openssl-1.0.2d
$ grep -R EVP_MD * | grep struct | egrep "(\.h|\.c)"
crypto/ossl_typ.h:typedef struct env_md_st EVP_MD;
crypto/ossl_typ.h:typedef struct env_md_ctx_st EVP_MD_CTX;
engines/ccgost/gost_lcl.h:/* EVP_MD structure for GOST R 34.11 */
engines/ccgost/gost_lcl.h:/* EVP_MD structure for GOST 28147 in MAC mode */
include/openssl/ossl_typ.h:typedef struct env_md_st EVP_MD;
include/openssl/ossl_typ.h:typedef struct env_md_ctx_st EVP_MD_CTX;
然后,在下面的struct env_md_ctx_st
:
$ grep -R "struct env_md_ctx_st" * | grep "{"
crypto/evp/evp.h:struct env_md_ctx_st {
include/openssl/evp.h:struct env_md_ctx_st {
最后,从第260行附近的evp.h
:
struct env_md_ctx_st {
const EVP_MD *digest;
ENGINE *engine; /* functional reference if 'digest' is
* ENGINE-provided */
unsigned long flags;
void *md_data;
/* Public key context for sign/verify */
EVP_PKEY_CTX *pctx;
/* Update function: usually copied from EVP_MD */
int (*update) (EVP_MD_CTX *ctx, const void *data, size_t count);
} /* EVP_MD_CTX */ ;
这是第160行的相关结构:
struct env_md_st {
int type;
int pkey_type;
int md_size;
unsigned long flags;
int (*init) (EVP_MD_CTX *ctx);
int (*update) (EVP_MD_CTX *ctx, const void *data, size_t count);
int (*final) (EVP_MD_CTX *ctx, unsigned char *md);
int (*copy) (EVP_MD_CTX *to, const EVP_MD_CTX *from);
int (*cleanup) (EVP_MD_CTX *ctx);
/* FIXME: prototype these some day */
int (*sign) (int type, const unsigned char *m, unsigned int m_length,
unsigned char *sigret, unsigned int *siglen, void *key);
int (*verify) (int type, const unsigned char *m, unsigned int m_length,
const unsigned char *sigbuf, unsigned int siglen,
void *key);
int required_pkey_type[5]; /* EVP_PKEY_xxx */
int block_size;
int ctx_size; /* how big does the ctx->md_data need to be */
/* control function */
int (*md_ctrl) (EVP_MD_CTX *ctx, int cmd, int p1, void *p2);
} /* EVP_MD */ ;