'openssl' is not recognized as internal or external command

Just you need to Add OpenSSL bin path (ex: C:\Program Files\OpenSSL-Win64\bin) to the PATH system variable as shown below:

install openssl for windows from the following link .

https://code.google.com/p/openssl-for-windows/downloads/detail?name=openssl-0.9.8k_WIN32.zip

The error you saw means there's no such program in your %PATH% (external command) and it's also not a built-in shell command (internal command).

Install OpenSSL on your machine. You will also need to check that its installed location is in your %PATH%. By default it probably won't be. As an example, suppose OpenSSL is installed at c:\OpenSSL-Win32. The openssl binary is probably located at c:\OpenSSL-Win32\bin\openssl.exe. So you path needs to include c:\OpenSSL-Win32\bin.

Sometimes OpenSSL cannot find its configuration file on Windows. For that, see OpenSSL and error in reading openssl.conf file.

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Another option is to use the full path in the command:

keytool -exportcert -alias androiddebugkey -keystore "<path-to-users-directory>\.android\debug.keystore" | ^
  c:\OpenSSL-Win32\bin\openssl.exe sha1 -binary | c:\OpenSSL-Win32\bin\openssl.exe base64

However, this still suffers the OpenSSL configuration file problem detailed at OpenSSL and error in reading openssl.conf file.