From ee2a527ec332ced4eee237b9f752519ce0a92c4d Mon Sep 17 00:00:00 2001
From: siddharth <s@ricketyspace.net>
Date: Sat, 16 Oct 2021 23:03:48 -0400
Subject: challenge: do challenge 31

---
 challenge/c31.go | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 172 insertions(+)
 create mode 100644 challenge/c31.go

(limited to 'challenge')

diff --git a/challenge/c31.go b/challenge/c31.go
new file mode 100644
index 0000000..d97fe11
--- /dev/null
+++ b/challenge/c31.go
@@ -0,0 +1,172 @@
+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package challenge
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"ricketyspace.net/cryptopals/lib"
+)
+
+func C31(serve bool) {
+	// In-Secure Byte Compare.
+	insecureCompare := func(a, b []byte) bool {
+		for i := 0; i < len(a); i++ {
+			if len(b) <= i {
+				return false
+			}
+			if a[i] != b[i] {
+				return false
+			}
+			lib.Sleep(50000000) // Sleep 50ms
+		}
+		return true
+	}
+
+	// HMAC HTTP Server.
+	httpServer := func() {
+		// Secret for HMAC
+		sec := lib.StrToBytes("Rae Street")
+
+		// Signature checkker.
+		sigCheck := func(f, s string) bool {
+			// Check signature.
+			h := lib.HmacSha1(sec, lib.StrToBytes(f))
+
+			if insecureCompare(h, lib.HexStrToBytes(s)) {
+				return true
+			}
+			return false
+		}
+
+		// HTTP Handler.
+		http.HandleFunc("/test", func(w http.ResponseWriter, r *http.Request) {
+			// Read query.
+			var f, s []string
+			var ok bool
+			q := r.URL.Query()
+			if f, ok = q["file"]; !ok {
+				w.WriteHeader(400)
+				fmt.Fprintf(w, "file not specified\n")
+				return
+			}
+			if len(f) > 1 {
+				w.WriteHeader(400)
+				fmt.Fprintf(w, "Cannot specify more than one file\n")
+				return
+			}
+			if s, ok = q["signature"]; !ok {
+				w.WriteHeader(400)
+				fmt.Fprintf(w, "signature not specified\n")
+				return
+			}
+			if len(s) > 1 {
+				w.WriteHeader(400)
+				fmt.Fprintf(w,
+					"Cannot specify more than one signature\n")
+				return
+			}
+			if !sigCheck(f[0], s[0]) {
+				w.WriteHeader(500) // Signature check failed.
+			}
+		})
+
+		// Start HTTP Server
+		http.ListenAndServe(":9000", nil)
+	}
+
+	// Makes HTTP POST request to the server.
+	makeRequest := func(f, s string) int {
+		// Make HTTP request.
+		q := fmt.Sprintf("file=%s&signature=%s", f, s)
+		u, err := url.Parse("http://localhost:9000/test?" + q)
+		if err != nil {
+			fmt.Printf("url parse failed: %v\n", err)
+			return 0
+		}
+		res, err := http.Post(u.String(), "text/plain", nil)
+		if err != nil {
+			fmt.Printf("http post failed: %v\n", err)
+			return res.StatusCode
+		}
+		return res.StatusCode
+	}
+
+	// Crack signature for file "foo".
+	crack := func() {
+		stc := time.Now() // Start time of crack
+
+		f := "foo"            // File
+		s := make([]byte, 20) // Signature
+
+		i := 0
+		g := byte(0)    // Guess byte.
+		tl := int64(50) // Time limit.
+		tries := 0
+		for {
+			st := time.Now()
+			sc := makeRequest(f, lib.BytesToHexStr(s))
+			et := time.Now().Sub(st) // Elapsed time.
+
+			if sc == 200 {
+				fmt.Printf("Signature Cracked: %x"+
+					" [tot. elapsed time: %v]\n",
+					s, time.Now().Sub(stc))
+				break
+			}
+			if et.Milliseconds() >= tl {
+				if tries < 5 { // Try guess at least 5 times.
+					tries += 1
+					continue
+				}
+				fmt.Printf("Signature Cracked Status: %x"+
+					" [tot. elapsed time: %v]\n",
+					s, time.Now().Sub(stc))
+				tl = et.Milliseconds() + 50
+				g = 0
+				i += 1
+				tries = 0
+			} else {
+				g += 1   // Change guess.
+				s[i] = g // Set guess.
+			}
+		}
+	}
+
+	if serve {
+		httpServer()
+	} else {
+		crack()
+	}
+}
+
+// Output:
+//
+// # Server:
+// $ ./cryptopals -c 31 -s
+// # Client:
+// $ ./cryptopals -c 31
+// Signature Cracked Status: 4400000000000000000000000000000000000000 [tot. elapsed time: 370.025362ms]
+// Signature Cracked Status: 44ee000000000000000000000000000000000000 [tot. elapsed time: 15.370118297s]
+// Signature Cracked Status: 44ee570000000000000000000000000000000000 [tot. elapsed time: 26.920301887s]
+// Signature Cracked Status: 44ee574500000000000000000000000000000000 [tot. elapsed time: 40.79052969s]
+// Signature Cracked Status: 44ee5745d3000000000000000000000000000000 [tot. elapsed time: 1m33.240732048s]
+// Signature Cracked Status: 44ee5745d3240000000000000000000000000000 [tot. elapsed time: 1m46.200916778s]
+// Signature Cracked Status: 44ee5745d324fd00000000000000000000000000 [tot. elapsed time: 3m20.301607262s]
+// Signature Cracked Status: 44ee5745d324fda7000000000000000000000000 [tot. elapsed time: 4m33.312205527s]
+// Signature Cracked Status: 44ee5745d324fda71e0000000000000000000000 [tot. elapsed time: 4m50.952330999s]
+// Signature Cracked Status: 44ee5745d324fda71ec000000000000000000000 [tot. elapsed time: 6m38.743155826s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cb000000000000000000 [tot. elapsed time: 8m45.094213819s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd0000000000000000 [tot. elapsed time: 11m15.26538765s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e00000000000000 [tot. elapsed time: 12m51.226137697s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c000000000000 [tot. elapsed time: 13m5.626232024s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c620000000000 [tot. elapsed time: 14m33.976999266s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c621c00000000 [tot. elapsed time: 15m4.937197749s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c621c70000000 [tot. elapsed time: 16m58.588103335s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c621c70ba0000 [tot. elapsed time: 20m15.459696698s]
+// Signature Cracked Status: 44ee5745d324fda71ec0cbdd7e0c621c70bae700 [tot. elapsed time: 24m33.111719984s]
+// Signature Cracked: 44ee5745d324fda71ec0cbdd7e0c621c70bae785 [tot. elapsed time: 27m7.782947967s]
-- 
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