# Tag Info

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What do you mean that you keep the root of the merkle tree locally? Is the merkle tree signed? If i understand what you are saying correctly, then the server can choose not to display to the public the changes you have made and keep presenting the merkle tree for the values before you updated them. Even if you sign the merkle tree the server can still do ...

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SHA-1 is measurably faster and I would like to know if its insecurity is still there, when used in a Merkle tree. Yes, the insecurity is still there. Any collision in the underlying hash function can be used to produce a collision in the root of the Merkle tree. A quick example: Suppose our SHA-1 Merkle tree has two leaf nodes, $a$ and $b$, and that ...

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Given only the information in the original question, it would be easy for an attacker to calculate generate an arbitrary message E, then calculate the Hash("This is message E + ab3ed") = 31415, and if the system can be tricked into trusting that 31415 is the hash of a valid message, there's no way to prove that E isn't really a valid sibling of B. This may ...

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I would like to extend Chrystographer answer. If this is a part of a incoming or outgoing message, you cannot prove it. Anybody can write valid messages. You need Merkle tree and digital signature of the root's hash.

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If your data is a set $S$ of key-value pairs, such that $S = \{(k,v) \vert k \in K, v \in V\}$, you can have non-membership proofs for your data by using a sorted Merkle tree (sorted by the keys in $K$). This tree can be a binary-search tree, a trie, a sparse Merkle Tree (similar to the one in Micali's Zero Knowledge sets paper, and also reintroduced by ...

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Merkle trees do not provide the option for a "non-membership-proof". However, as the user knows the whole tree in your case, the server can just send the hash of the element (or the element itself, depending on how you construct the leafs). The user can verify that the hash is unequal to every leaf of the tree. While this is still not very efficient (linear ...

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If you are not worried about revealing information, then you can commit to the set of data items in one Merkle tree, and to the frontier of that set in another Merkle tree. A frontier is the set of ancestors to all values that are not in the tree (note that this is about the same size as the size of the set itself). Then, in order to prove that a value is ...

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