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Nonsecure hash algorithm

Context used for message digest creation is associated with weak algorithm

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Description

This defect occurs when you use a cryptographic hash function that is proven to be weak against certain forms of attack.

The hash functions flagged by this checker include SHA-0, SHA-1, MD4, MD5, and RIPEMD-160. The checker detects the use of these hash functions in:

  • Functions from the EVP API such as EVP_DigestUpdate or EVP_SignUpdate.

  • Functions from the low level API such as SHA1_Update or MD5_Update.

Risk

You use a hash function to create a message digest from input data and thereby ensure integrity of your data. The hash functions flagged by this checker use algorithms with known weaknesses that an attacker can exploit. The attacks can comprise the integrity of your data.

Fix

Use a more secure hash function. For instance, use the later SHA functions such as SHA-224, SHA-256, SHA-384, and SHA-512.

Examples

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#include <openssl/evp.h>

#define fatal_error() exit(-1)

int ret;
unsigned char *out_buf;
unsigned int out_len;

void func(unsigned char *src, size_t len, EVP_PKEY* pkey){
  EVP_MD_CTX* ctx = EVP_MD_CTX_create();

  ret = EVP_SignInit_ex(ctx, EVP_md5(), NULL);
  if (ret != 1) fatal_error();

  ret = EVP_DigestUpdate(ctx,src,len);

  if (ret != 1) fatal_error();

  ret = EVP_SignFinal(ctx, out_buf, &out_len, pkey);
  if (ret != 1) fatal_error();
}

In this example, during initialization with EVP_SignInit_ex, the context object is associated with the weak hash function MD5. The checker flags the usage of this context in the update step with EVP_DigestUpdate.

Correction — Use SHA-2 Family Function

One possible correction is to use a hash function from the SHA-2 family, such as SHA-256.

#include <openssl/evp.h>

#define fatal_error() exit(-1)

int ret;
unsigned char *out_buf;
unsigned int out_len;

void func(unsigned char *src, size_t len, EVP_PKEY* pkey){
  EVP_MD_CTX* ctx = EVP_MD_CTX_create();

  ret = EVP_SignInit_ex(ctx, EVP_sha256(), NULL); 
  if (ret != 1) fatal_error();

  ret = EVP_SignUpdate(ctx, src, len); 
  if (ret != 1) fatal_error();

  ret = EVP_SignFinal(ctx, out_buf, &out_len, pkey);
  if (ret != 1) fatal_error();
}

Result Information

Group: Cryptography
Language: C | C++
Default: Off
Command-Line Syntax: CRYPTO_MD_WEAK_HASH
Impact: Medium

Version History

Introduced in R2018a

See Also

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