Rpi Datasheet 701 Downloading OS Images

SHA checksums 

SHA Checksums are usually shown as a long series of numbers that represent the value that was calculated when a mathmatical calculation was performed on the contents of a file that has been made available for download. The checksum is used to verify that the content is authentic and has neither been altered by an unauthorized third party, nor been damaged during the transfer process across the Internet.

The checksums used on the Raspberry Pi download site use SHA-1. The SHA-1 algorithm is a 160-bit hash function which resembles the earlier MD5 algorithm. This was designed by the National Security Agency (NSA) to be part of the Digital Signature Algorithm.

Linux Instructions: 

1. Download the image file from the Raspberry Pi website 2. Go to a Linux terminal (Shell prompt)) 3. Run sha1sum /path/to/file 4. If it's not there go back to step 3 and start again 5. Compare the hash you have with the one on the site 6. If they are the same... great success 7. If not, go back to step 1

Windows Instructions: 

1. Download the image file from the Raspberry Pi website 2. Download sha1sum.exe from http://downloads.raspberrypi.org/tools/sha1sum.exe 3. Open command prompt (DOS prompt) and drag and drop the sha1sum.exe in to the command prompt (and it will display the path to the file sha1sum.exe file), then you just put a space, drag the image file into the command prompt too and press enter compare result with one on site 4. If it's not there go back to step 3 and start again 5. Compare the hash you have with the one on the site 6. If they are the same... great success 7. If not, go back to step 1

MAC Instructions: 

1. Download the image file from the Raspberry Pi website and make sure you have the icon of the downloaded file displayed somewhere in the Finder. 2. Open the Terminal application. 3. Run "/usr/bin/openssl sha1" (without the quotes), then you just put a space, drag the image file into the command prompt too and press enter 4. If it's not there go back to step 3 and start again 5. Compare the hash you have with the one on the site 6. If they are the same... great success 7. If not, go back to step 1