challenge: do challenge 22

3 files changed, 69 insertions, 0 deletions

diff --git a/challenge/c22.go b/challenge/c22.go
new file mode 100644
index 0000000..603cb9e
--- /dev/null
+++ b/challenge/c22.go
@@ -0,0 +1,56 @@
+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package challenge
+
+import (
+	"fmt"
+	"time"
+
+	"ricketyspace.net/cryptopals/lib"
+)
+
+func C22() {
+	minWait := 40 * time.Second
+	maxWait := 1000 * time.Second
+	randomWait := func() {
+		fmt.Printf("Waiting for a random amount of time...\n")
+		s := time.Now()
+		lib.SleepRandom(minWait, maxWait)
+		fmt.Printf("Elapsed time %v\n", time.Now().Sub(s))
+	}
+
+	fmt.Printf("This challenge might take ~%v to ~%v to complete\n",
+		2*minWait, 2*maxWait)
+
+	randomWait()
+	fmt.Printf("Generating seed from current time...\n")
+	lib.MTSeed(uint32(time.Now().Unix()))
+	randomWait()
+
+	fmt.Printf("Extracting first random 32-bit garbage fron RNG...\n")
+	random := lib.MTExtract()
+
+	fmt.Printf("Cracking seed...\n")
+	guess := uint32(time.Now().Unix())
+	for {
+		lib.MTSeed(guess)
+		x := lib.MTExtract()
+		if x == random {
+			fmt.Printf("Found seed %v\n", guess)
+			break
+		}
+		guess = guess - 1
+	}
+}
+
+// Output:
+// This challenge might take ~1m20s to ~33m20s to complete
+// Waiting for a random amount of time...
+// Elapsed time 10m51.671176141s
+// Generating seed from current time...
+// Waiting for a random amount of time...
+// Elapsed time 14m48.257182374s
+// Extracting first random 32-bit garbage fron RNG...
+// Cracking seed...
+// Found seed 1625112975
diff --git a/cryptopals.go b/cryptopals.go
index 98b6759..4767a37 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -61,5 +61,7 @@ func main() {
 		challenge.C20()
 	case 21:
 		challenge.C21()
+	case 22:
+		challenge.C22()
 	}
 }
diff --git a/lib/time.go b/lib/time.go
new file mode 100644
index 0000000..dbeb843
--- /dev/null
+++ b/lib/time.go
@@ -0,0 +1,11 @@
+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+import "time"
+
+// Sleeps for atleast `min` but not more than `max`.
+func SleepRandom(min, max time.Duration) {
+	time.Sleep(time.Duration(RandomInt(int64(min), int64(max))))
+}