Generate sha256 with OpenSSL and C

Question

I m looking to create a hash with sha256 using openssl and C    I know there s a similar post at Generate SHA hash in C   using OpenSSL library  but I m looking to specifically create sha256   UPDATE    Seems to be a problem with the include paths  It can t find any OpenSSL functions even though I included    include  openssl sha h    and I included the paths in my build  -I opt ssl include  -L opt ssl lib  -lcrypto

User · Accepted Answer

Here s how I did it   void sha256 hash string  unsigned char hash SHA256 DIGEST LENGTH   char outputBuffer 65         int i   0       for i   0  i  lt  SHA256 DIGEST LENGTH  i                  sprintf outputBuffer    i   2     02x   hash i               outputBuffer 64    0      void sha256 string char  string  char outputBuffer 65         unsigned char hash SHA256 DIGEST LENGTH       SHA256 CTX sha256      SHA256 Init  amp sha256       SHA256 Update  amp sha256  string  strlen string        SHA256 Final hash   amp sha256       int i   0      for i   0  i  lt  SHA256 DIGEST LENGTH  i                  sprintf outputBuffer    i   2     02x   hash i              outputBuffer 64    0     int sha256 file char  path  char outputBuffer 65         FILE  file   fopen path   rb        if  file  return -534       unsigned char hash SHA256 DIGEST LENGTH       SHA256 CTX sha256      SHA256 Init  amp sha256       const int bufSize   32768      unsigned char  buffer   malloc bufSize       int bytesRead   0      if  buffer  return ENOMEM      while  bytesRead   fread buffer  1  bufSize  file                  SHA256 Update  amp sha256  buffer  bytesRead             SHA256 Final hash   amp sha256        sha256 hash string hash  outputBuffer       fclose file       free buffer       return 0      It s called like this   static unsigned char buffer 65   sha256  string   buffer   printf   s n   buffer

User · Answer

Here s the function I personally use - I simply derived it from the function I used for sha-1 hashing  char  str2sha256  const char  str  int length       int n    SHA256 CTX c    unsigned char digest  SHA256 DIGEST LENGTH      char  out    char   malloc  33       SHA256 Init   amp c       while   length  gt  0         if   length  gt  512   SHA256 Update   amp c  str  512        else SHA256 Update   amp c  str  length         length -  512      str    512         SHA256 Final   digest   amp c       for   n   0  n  lt  SHA256 DIGEST LENGTH    n       snprintf   amp   out  n 2      16 2   quot  02x quot    unsigned int  digest  n         return out

User · Answer

I think that you only have to replace SHA1 function with SHA256 function with tatk code from link in Your post

User · Answer

Using OpenSSL s EVP interface  the following is for OpenSSL 1 1     include  lt iomanip gt   include  lt iostream gt   include  lt sstream gt   include  lt string gt   include  lt openssl evp h gt   bool computeHash const std  string amp  unhashed  std  string amp  hashed        bool success   false       EVP MD CTX  context   EVP MD CTX new         if context    NULL                if EVP DigestInit ex context  EVP sha256    NULL                         if EVP DigestUpdate context  unhashed c str    unhashed length                                   unsigned char hash EVP MAX MD SIZE                   unsigned int lengthOfHash   0                   if EVP DigestFinal ex context  hash   amp lengthOfHash                                         std  stringstream ss                      for unsigned int i   0  i  lt  lengthOfHash    i                                                ss  lt  lt  std  hex  lt  lt  std  setw 2   lt  lt  std  setfill  0    lt  lt   int hash i                                              hashed   ss str                        success   true                                                     EVP MD CTX free context              return success     int main int  char          std  string pw1    password1   pw1hashed      std  string pw2    password2   pw2hashed      std  string pw3    password3   pw3hashed      std  string pw4    password4   pw4hashed       hashPassword pw1  pw1hashed       hashPassword pw2  pw2hashed       hashPassword pw3  pw3hashed       hashPassword pw4  pw4hashed        std  cout  lt  lt  pw1hashed  lt  lt  std  endl      std  cout  lt  lt  pw2hashed  lt  lt  std  endl      std  cout  lt  lt  pw3hashed  lt  lt  std  endl      std  cout  lt  lt  pw4hashed  lt  lt  std  endl       return 0      The advantage of this higher level interface is that you simply need to swap out the EVP sha256   call with another digest s function  e g  EVP sha512    to use a different digest  So it adds some flexibility

User · Answer

std based   include  lt iostream gt   include  lt iomanip gt   include  lt sstream gt   include  lt string gt   using namespace std    include  lt openssl sha h gt  string sha256 const string str        unsigned char hash SHA256 DIGEST LENGTH       SHA256 CTX sha256      SHA256 Init  amp sha256       SHA256 Update  amp sha256  str c str    str size         SHA256 Final hash   amp sha256       stringstream ss      for int i   0  i  lt  SHA256 DIGEST LENGTH  i                  ss  lt  lt  hex  lt  lt  setw 2   lt  lt  setfill  0    lt  lt   int hash i             return ss str       int main         cout  lt  lt  sha256  1234567890 1    lt  lt  endl      cout  lt  lt  sha256  1234567890 2    lt  lt  endl      cout  lt  lt  sha256  1234567890 3    lt  lt  endl      cout  lt  lt  sha256  1234567890 4    lt  lt  endl      return 0

User · Answer

A more  C   ish version   include  lt iostream gt   include  lt sstream gt    include  openssl sha h   using namespace std   string to hex unsigned char s        stringstream ss      ss  lt  lt  hex  lt  lt   int  s      return ss str          string sha256 string line            unsigned char hash SHA256 DIGEST LENGTH       SHA256 CTX sha256      SHA256 Init  amp sha256       SHA256 Update  amp sha256  line c str    line length         SHA256 Final hash   amp sha256        string output               for int i   0  i  lt  SHA256 DIGEST LENGTH  i              output    to hex hash i              return output     int main         cout  lt  lt  sha256  hello  world    lt  lt  endl       return 0

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