No, you are not leaking any information except how to MAC those specific values with the specific key you are using. Using a short message is exactly as secure as using a long message.

For the following, remember the definition HMAC (K,m) = H((K ⊕ opad) || H((K ⊕ ipad) || m)). There are two hashes here, an outer hash and an inner hash nested inside the outer one. The message is inside the inner hash.

Suppose I am an attacker who has your message and MAC result, and I want to derive your key. In order to get your key, I will need to do a brute-force guess. I already know the function H, I know the constants ipad and opad, and I know your message m. I need to try building lots of hashes using different key values until I come up with the right HMAC. The hardness of this task is dependent entirely on the length of K; the length of m is not a factor.

Note, however, that if you are not using a temporary key, then any message/HMAC pairs you give out you will be valid for your key, so an attacked could impersonate you in a replay attack for any messages she has seen from you.

No, you are not leaking any information except how to MAC those specific values with the specific key you are using. Using a short message is exactly as secure as using a long message.

For the following, remember the definition HMAC (K,m) = H((K ⊕ opad) || H((K ⊕ ipad) || m)). There are two hashes here, an outer hash and an inner hash nested inside the outer one. The message is inside the inner hash.

Suppose I am an attacker who has your message and MAC result, and I want to derive your key. In order to get your key, I will need to do a brute-force guess. I already know the function H, I know the constants ipad and opad, and I know your message m. I need to try building lots of hashes using different key values until I come up with the right HMAC. The hardness of this task is dependent entirely on the length of K; the length of m is not a factor.

Note, however, that if you are not using a temporary key, then any message/HMAC pairs you give out will be valid for your key, so an attacker could impersonate you in a replay attack for any messages she has seen from you.

No, you are not leaking any information except how to MAC those specific values with the specific key you are using. Using a short message is exactly as secure as using a long message.

For the following, remember the definition HMAC (K,m) = H((K ⊕ opad) || H((K ⊕ ipad) || m)). There are two hashes here, an outer hash and an inner hash nested inside the outer one. The message is inside the inner hash.

Suppose I am an attacker who has your message and MAC result, and I want to derive your key. In order to get your key, I will need to do a brute-force guess. I already know the function H, I know the constants ipad and opad, and I know your message m. I need to try building lots of hashes using different key values until I come up with the right HMAC. The hardness of this task is dependent entirely on the length of K; the length of m is not a factor.

No, you are not leaking any information except how to MAC those specific values with the specific key you are using. Using a short message is exactly as secure as using a long message.

For the following, remember the definition HMAC (K,m) = H((K ⊕ opad) || H((K ⊕ ipad) || m)). There are two hashes here, an outer hash and an inner hash nested inside the outer one. The message is inside the inner hash.

Suppose I am an attacker who has your message and MAC result, and I want to derive your key. In order to get your key, I will need to do a brute-force guess. I already know the function H, I know the constants ipad and opad, and I know your message m. I need to try building lots of hashes using different key values until I come up with the right HMAC. The hardness of this task is dependent entirely on the length of K; the length of m is not a factor.

Note, however, that if you are not using a temporary key, then any message/HMAC pairs you give out you will be valid for your key, so an attacked could impersonate you in a replay attack for any messages she has seen from you.