Let's suppose you can use a character set of, say, 40 symbols of unambiguous upper,lower and numeric characters.

For a sequence of n chars, you've got 40^n combinations

• 40^4 = 2,560,000
• 40^5 = 102,400,000
• 40^6 = 4,096,000,000
• 40^7 = 163,840,000,000
• 40^8 = 6,553,600,000,000

Thus 8 chars gives a pretty good space to work in - if you generated 10 million codes, you'd have to try hundreds of thousands of combinations to brute force a code.

Or you come at from the other direction - give the number of possible codes, how many codes should you generate to avoid the trap they call the Birthday Paradox?

Taking the 8 char code, 6,553,600,000,000 is approx 2^42, thus you might reasonably generate 2^21 codes from it, or 2,097,152

Let's suppose you can use a character set of, say, 40 symbols of unambiguous upper,lower and numeric characters.

For a sequence of n chars, you've got 40ⁿ combinations

• 40⁴ = 2,560,000
• 40⁵ = 102,400,000
• 40⁶ = 4,096,000,000
• 40⁷ = 163,840,000,000
• 40⁸ = 6,553,600,000,000

Thus 8 chars gives a pretty good space to work in - if you generated 10 million codes, you'd have to try hundreds of thousands of combinations to brute force a code.

Or you come at from the other direction - give the number of possible codes, how many codes should you generate to avoid the trap they call the Birthday Paradox?

Taking the 8 char code, 6,553,600,000,000 is approx 2⁴², thus you might reasonably generate 2²¹ codes from it, or 2,097,152

Let's suppose you can use a character set of, say, 40 symbols of unambiguous upper,lower and numeric characters.

For a sequence of n chars, you've got 40^n combinations

• 40^4 = 2,560,000
• 40^5 = 102,400,000
• 40^6 = 4,096,000,000
• 40^7 = 163,840,000,000
• 40^8 = 6,553,600,000,000

Thus 8 chars gives a pretty good space to work in - if you generated 10 million codes, you'd have to try hundreds of thousands of combinations to brute force a code.

Let's suppose you can use a character set of, say, 40 symbols of unambiguous upper,lower and numeric characters.

For a sequence of n chars, you've got 40^n combinations

• 40^4 = 2,560,000
• 40^5 = 102,400,000
• 40^6 = 4,096,000,000
• 40^7 = 163,840,000,000
• 40^8 = 6,553,600,000,000

Thus 8 chars gives a pretty good space to work in - if you generated 10 million codes, you'd have to try hundreds of thousands of combinations to brute force a code.

Or you come at from the other direction - give the number of possible codes, how many codes should you generate to avoid the trap they call the Birthday Paradox?

Taking the 8 char code, 6,553,600,000,000 is approx 2^42, thus you might reasonably generate 2^21 codes from it, or 2,097,152