Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, on PasswordsGenerator.net.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "nonce".

Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, on PasswordsGenerator.net.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "nonce".

Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, here.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "nonce".

Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, on PasswordsGenerator.net.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "nonce".

Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, here.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "salt".

Have Alice generate and publish an SHA-256 hash of her action.

SHA-256 is a computationally-secure (to reasonable approximation) algorithm that converts a given string into an unintelligible hexadecimal hash. There are online implementations that will compute SHA256 for you, for instance, here.

The idea is this:

1. Alice decides her action - say, "I cast Fireball at Bob"
2. Alice privately records that exact text
3. Alice enters that text into an SHA256 generator, producing a meaningless jumble of characters - A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E
4. Alice publicly announces "I've planned an action; its SHA-256 is A0FC4543FDBA266006F1F9FA818183710A8C5CA80613DA109B8A9DBA194DEC4E"

Now, Bob cannot tell what Alice has planned because the SHA-256 is not reversible; there's no way to get from the hash back to the action.

Later, when Alice reveals her plan, she gives the exact text she prepared earlier. If Bob doesn't trust her, he can simply repeat the SHA-256 encryption, and verify that the signatures match.

If Alice suspects that Bob may guess her action, then she can make things harder by adding an extra, irrelevant component to the action before computing the SHA-256. For instance, if Alice records, signs, and later reveals "I cast Fireball at Bob (pistachio)", then Bob would not be able to guess and verify the action without also guessing the extra "(pistachio)". This is known as using a "nonce".