Generate SHA hash in C using OpenSSL library

Question

How can I generate SHA1 or SHA2 hashes using the OpenSSL libarary   I searched google and could not find any function or example code

User · Answer

Adaptation of  AndiDog version for big file   static const int K READ BUF SIZE  1024   16     std  optional lt std  string gt  CalcSha256 std  string filename           Initialize openssl     SHA256 CTX context      if  SHA256 Init  amp context                 return std  nullopt                Read file and update calculated SHA     char buf K READ BUF SIZE       std  ifstream file filename  std  ifstream  binary       while  file good                  file read buf  sizeof buf            if  SHA256 Update  amp context  buf  file gcount                           return std  nullopt                          Get Final SHA     unsigned char result SHA256 DIGEST LENGTH       if  SHA256 Final result   amp context                 return std  nullopt                Transform byte-array to string     std  stringstream shastr      shastr  lt  lt  std  hex  lt  lt  std  setfill  0        for  const auto  amp byte  result                shastr  lt  lt  std  setw 2   lt  lt   int byte            return shastr str

User · Answer

correct syntax at command line should be  echo -n  compute sha1    openssl sha1   otherwise you ll hash the trailing newline character as well

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From the command line  it s simply   printf  compute sha1    openssl sha1   You can invoke the library like this    include  lt stdio h gt   include  lt string h gt   include  lt openssl sha h gt   int main         unsigned char ibuf      compute sha1       unsigned char obuf 20        SHA1 ibuf  strlen ibuf   obuf        int i      for  i   0  i  lt  20  i              printf   02x    obuf i              printf   n         return 0

User · Answer

OpenSSL has a horrible documentation with no code examples  but here you are    include  lt openssl sha h gt   bool simpleSHA256 void  input  unsigned long length  unsigned char  md        SHA256 CTX context      if  SHA256 Init  amp context           return false       if  SHA256 Update  amp context   unsigned char  input  length           return false       if  SHA256 Final md   amp context           return false       return true      Usage   unsigned char md SHA256 DIGEST LENGTH      32 bytes if  simpleSHA256  lt data buffer gt    lt data length gt   md            handle error     Afterwards  md will contain the binary SHA-256 message digest  Similar code can be used for the other SHA family members  just replace  256  in the code   If you have larger data  you of course should feed data chunks as they arrive  multiple SHA256 Update calls

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C version of  Nayfe code  generating SHA1 hash from file    include  lt stdio h gt   include  lt openssl sha h gt   static const int K READ BUF SIZE     1024   16    unsigned char  calculateSHA1 char  filename        if   filename            return NULL             FILE  fp   fopen filename   rb        if  fp    NULL            return NULL             unsigned char  sha1 digest   malloc sizeof char  SHA DIGEST LENGTH       SHA CTX context       if  SHA1 Init  amp context           return NULL       unsigned char buf K READ BUF SIZE       while   feof fp                 size t total read   fread buf  1  sizeof buf   fp           if  SHA1 Update  amp context  buf  total read                         return NULL                      fclose fp        if  SHA1 Final sha1 digest   amp context           return NULL       return sha1 digest      It can be used as follows   unsigned char  sha1digest   calculateSHA1   tmp file1      The res variable contains the sha1 hash   You can print it on the screen using the following for-loop   char  sha1hash    char   malloc sizeof char    41   sha1hash 41      0   int i  for  i   0  i  lt  SHA DIGEST LENGTH  i          sprintf  amp sha1hash i 2     02x   sha1digest i      printf  SHA1 HASH   s n   sha1hash

User · Answer

Here is OpenSSL example of calculating sha-1 digest using BIO    include  lt openssl bio h gt   include  lt openssl evp h gt   std  string sha1 const std  string  amp input        BIO   p bio md    nullptr      BIO   p bio mem   nullptr       try                  make chain  p bio md  lt - gt  p bio mem         p bio md   BIO new BIO f md             if   p bio md  throw std  bad alloc            BIO set md p bio md  EVP sha1              p bio mem   BIO new mem buf  void  input c str    input length             if   p bio mem  throw std  bad alloc            BIO push p bio md  p bio mem               read through p bio md            read sequence  buf  lt  lt -- p bio md  lt  lt -- p bio mem         std  vector lt char gt  buf input size             for                            auto nread   BIO read p bio md  buf data    buf size                 if  nread   lt  0    throw std  runtime error  BIO read failed                  if  nread    0    break       eof                       get result         char md buf EVP MAX MD SIZE           auto md len   BIO gets p bio md  md buf  sizeof md buf            if  md len  lt   0    throw std  runtime error  BIO gets failed               std  string result md buf  md len               clean         BIO free all p bio md            return result            catch                     if  p bio md    BIO free all p bio md             throw            Though it s longer than just calling SHA1 function from OpenSSL  but it s more universal and can be reworked for using with file streams  thus processing data of any length

[c++] Generate SHA hash in C++ using OpenSSL library

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