feat: add sha256_length_extension_attacks

sha256_length_extension_attacks/README.md

@@ -0,0 +1,26 @@
+> Copied from: https://github.com/skerkour/kerkour.com/tree/main/blog/2023/sha256_length_extension_attacks
+
+# [Breaking SHA256: length extension attacks in practice](https://kerkour.com/sha256-length-extension-attacks)
+
+
+## Usage
+
+```bash
+$ go run ./ -verbose
+SecretKey: 7365637265747365637265747365637265747365637265747365637265747365
+Legitimate Data: user_id=1&role=user
+Legitimate Signature SHA256(SecretKey || LegitimateData): 5b0b4b2472778fea87faac08a72a47d24538bff9d7f19a3a85d069893e2b08ab
+Verify LegitimateSignature == SHA256(SecretKey || LegitimateData): true
+
+---------------------------------------------------------------------------------------------------
+
+Malicious Data: &something=true&role=admin
+Malicious Message (LegitimateData || padding || MaliciousData):
+00000000  75 73 65 72 5f 69 64 3d  31 26 72 6f 6c 65 3d 75  |user_id=1&role=u|
+00000010  73 65 72 80 00 00 00 00  00 00 00 00 00 00 01 98  |ser.............|
+00000020  26 73 6f 6d 65 74 68 69  6e 67 3d 74 72 75 65 26  |&something=true&|
+00000030  72 6f 6c 65 3d 61 64 6d  69 6e                    |role=admin|
+
+Malicious Signature: 8c37e11e8397b39cba72fa0e4769716c69a7ba9e29cfaf00d4601e086e85dd8f
+Verify MaliciousSignature == SHA256(SecretKey, MaliciousMessage): true
+```