System, method, and computer program for text sanitization

Abstract

A system, method, and computer program are provided for text sanitization. The system builds a corpus of document vectors (including tokenizing each document, creating a vector representation based on the tokens, and building a corpus of vector representations), obtains a new document for text sanitization, tokenizes the new document, creates a new document vector based on the tokens in the new document, and accesses the corpus of document vectors. The system filters each of the tokens in the new document against a privacy threshold. The system performs a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors. The system replaces or redacts the tokens in the document flagged as unsafe. The system updates the corpus of document vectors to include the new document vector in its form prior to the filtering and k-anonymity sanitization steps.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to document sanitization and, more specifically, to a system and method for automatically sanitizing text in heterogeneous documents.

2. Description of the Background Art

It is very useful for a business to be able to automate aspects of their customer service, thereby increasing efficiency and reducing required resources. Many such businesses employ Automatic Speech Recognition (ASR) systems and various user interface systems. In order to train the neural networks used to automate such systems, a lot of data from user interactions is needed. Unfortunately, the data used to train such systems often contains sensitive information, and it is difficult to determine which of the data is sensitive and which of the data is non-sensitive in nature. Known document sanitization techniques rely on the detection of specific information from concrete domains (e.g., credit card and social security numbers from particular databases). In other words, such techniques require customization for each domain and lack generality and scalability. Therefore, there is a need for a document sanitization method that performs automatically with respect to heterogenous documents.

Any such method would require a careful balance between how much data to redact and how much data to maintain. If a system over-redacts data, then the remaining data is less useful for training purposes. If the system does not redact enough, then it may leave sensitive information in the documents. Therefore, there is also a need to optimize redaction while removing any sensitive information, such that the data is still useful for training.

SUMMARY OF THE DISCLOSURE

The present disclosure describes a system, method, and computer program for text sanitization. The method is performed by a computer system that includes servers, storage systems, networks, operating systems, and databases.

The present invention provides a system and method for automatically sanitizing text in heterogeneous documents. It does this through three main sanitization steps with respect to a corpus of document vectors (i.e., vector representations of documents based on the tokens in the documents). First, the system filters tokens in a new document against a privacy threshold, where the tokens having a frequency in the corpus of document vectors below a threshold are flagged as unsafe. This is based on the principle that very infrequent words are likely to be sensitive information, but frequent words are likely to be common information. Second, the system performs a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors. While k-anonymity is a known technique, it is not well-understood, routine, or conventional in the field to combine it with privacy threshold filtering. Furthermore, it is challenging to select the optimal k-value such that the system redacts the minimum number of tokens. While a linear programming approach may be helpful in finding an optimal k vector, it is computationally very expensive. The present invention provides a heuristic approach to finding the near-optimal k vector, which is computationally much more efficient and, therefore, faster. Third, the system replaces or redacts the tokens in the document flagged as unsafe using a machine-learning language model to predict a vector representation.

In one embodiment, a method for text sanitization comprises the following steps:

• • building a corpus of document vectors by performing the following:
    • obtaining a plurality of documents;
    • tokenizing each of the plurality of documents;
    • for each of the plurality of documents, creating a vector representation of the document based on the tokens in the document;
    • building a corpus of document vectors comprising the vector representations for the plurality of documents;
  • obtaining a new document for text sanitization;
  • tokenizing the new document;
  • creating a new document vector based on the tokens in the new document;
  • accessing the corpus of document vectors;
  • filtering each of the tokens in the new document against a privacy threshold, wherein any tokens having a frequency in the corpus of document vectors below the privacy threshold are flagged as unsafe;
  • performing a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors, wherein k is a positive integer, and wherein, during the k-anonymity sanitization process, tokens in the document are flagged as either safe or unsafe;
  • replacing or redacting the tokens in the document flagged as unsafe; and
  • updating the corpus of document vectors to include the new document vector in its form prior to the filtering and k-anonymity sanitization steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart that illustrates a method, according to one embodiment, for privacy-preserving text sanitization.

FIGS. 2A-2B are flowcharts that illustrate the method of FIG. 1, according to one embodiment, in greater detail.

FIG. 3 is a graphical example of the methods of FIGS. 1-2B according to one embodiment.

FIGS. 4A-4B are flowcharts that illustrate a method, according to one embodiment, for a heuristic approach to k-anonymity sanitization of a document.

FIG. 5 is a flowchart that illustrates a method, according to one embodiment, for document sanitization.

FIG. 6 is a block diagram that illustrates an example system architecture according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present disclosure describes a system, method, and computer program for text sanitization. The method is performed by a computer system that includes servers, storage systems, networks, operating systems, and databases (“the system”).

Example implementations of the methods are described in more detail with respect to FIGS. 1-6

1. Method for Privacy-Preserving Text Sanitization

FIGS. 1 and 2A-2B illustrate a method for text sanitization. As illustrated in FIG. 1, in one embodiment, the text sanitization method includes the following steps: corpus building (step 110), receiving a new document for text sanitization (step 120), text preprocessing of the new document (step 130), privacy threshold filtering (step 140), k-anonymity sanitization using heuristics (step 150), document sanitization (step 160), and corpus updating (step 170). These steps are described in more detail with respect to FIGS. 2A-2B.

1.1 Corpus Building

As seen in FIG. 2A, the corpus building step from FIG. 1 includes the system obtaining a plurality of documents (step 205), where a document is a collection of words. For example, text generated during a time interval would be treated as a document. In a customer service setting, a document is formed by all the textual information shared during the resolution of an issue (e.g., a user-agent conversation, text rendered in the user interface of an application used by a customer service agent, etc.). The system tokenizes each of the plurality of documents (step 210). The system creates a vector representation of each of the plurality of documents (step 215). In certain embodiments, the vector representation of the document indicates the tokens present in the document. In certain embodiments, the vector representation includes a first bit value for each token in a vocabulary that is present in the document and a second bit value for each token in the vocabulary that is not present in the document. For example, the vector representation may include a “1” for each word the document contains and a “0” for each word the document does not contain. In certain embodiments, a vocabulary is the set of all the tokenized words that have been seen and inserted into the corpus of document vectors. In certain embodiments, the dimension of the vector is the whole vocabulary.

In certain embodiments, for each of the vector representations, the system creates an equivalent vector of cryptographically secure hashes (e.g., the equivalent vector is comprised of the SHA256 hash of each of the words in the original vector using a PBKDF2 approach) (step 220) and builds a corpus of document vectors comprising the equivalent vectors (step 225), where a corpus is a database of vectors. This allows for the original vector to be maintained without storing any sensitive information.

1.2 Text Preprocessing

The system receives a new document for text sanitization (step 230). As seen in FIG. 2B, the text preprocessing step of FIG. 1 includes the system tokenizing the new document (step 235). The system creates a vector representation of the new document based on the tokens in the new document (step 240). In certain embodiments, the system creates an equivalent vector of cryptographically secure hashes (step 245).

1.3 Privacy Threshold Filtering

The privacy threshold filtering step of FIG. 1 includes the system filtering the tokens in the new document against a privacy threshold (step 250). Any tokens having a frequency in the corpus of document vectors below the privacy threshold are flagged as unsafe. An example of a privacy threshold is p=0.005.

1.3 k-Anonymity Sanitization

The k-anonymity sanitization step of FIG. 1 includes the system performing a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors (step 255), as seen in greater detail with respect to FIGS. 4A-4B. In certain embodiments, k is a positive integer, and during the k-anonymity sanitization process, tokens in the document are flagged as either safe or unsafe. As mentioned above, a k-anonymity sanitization process is not often combined with a privacy filtering threshold. The unforeseen benefit of combining the two methods is that, whereas a system may, for example, typically use a k-value of 4, 5, or 6, combined with a privacy threshold filtering step, the k-value can be reduced to, for example, 2 or 3 and still receive optimal safety properties, but avoid over-redaction within a document.

1.4 Document Sanitization

The document sanitization step of FIG. 1 includes the system replacing or redacting words flagged as unsafe during the privacy threshold filtering and k-anonymity sanitization steps (step 260), as seen in greater detail with respect to FIG. 5.

1.5 Updating Corpus

The updating corpus step of FIG. 1 includes the system updating the corpus of document vectors to include the new (equivalent) document vector in its form prior to the filtering and k-anonymity sanitization steps (step 265).

1.6 Graphical Example

FIG. 3 illustrates a graphical example for the methods of text sanitization, including corpus building, text preprocessing of a new document, privacy threshold filtering, k-anonymity sanitization, and document sanitization. The steps show how a vector changes and what will be redacted. For example, in step 3, the second “1” has been changed to a “0” during the privacy threshold filtering step. This means that the token (or word) corresponding to the “1” is flagged as unsafe and will be replaced or redacted.

2. Method for Heuristic Approach to k-Anonymity Sanitization of a Document

FIGS. 4A-4B illustrate a method for a heuristic approach to k-anonymity sanitization of a document. The system computes the frequency of each token within the document (i.e., both the new document and the corpus of document vectors) (step 405). The system sorts the tokens according to an ordering criteria and begins processing the tokens (step 410). For example, the system may sort in descending order of frequency (from highest to lowest frequency), or the system may sort using another ordering criteria. In certain embodiments, a more elaborate ordering criteria may result in a more optimized solution, but at a higher computational cost. The system identifies a set S of documents, where initially the set is all the documents in the corpus of document vectors (step 415).

The system begins processing each token in the sorted list of tokens (in order) (step 420). The system identifies all other documents in the set S that include the token (step 425). The system determines if the number of documents is greater than k (step 430). If the system determines that the number of documents is not greater than k, the system flags the token as unsafe and proceeds to step 450 (step 435). If the system determines that the number of documents is greater than k, the system flags the token as safe (step 440).

If the token being processed is flagged as safe, the system updates set S by removing all documents not having the token from S (step 445). If, however, the token is flagged as unsafe, the system leaves set S unchanged. The system determines whether there is another token for processing (step 450). If the system determines that there is another token for processing, the system returns to step 420 to begin processing the next token (step 455). If the system determines there is no other token for processing, the k-anonymity sanitization is complete (step 460). When the words flagged as unsafe are redacted, the document will be indistinguishable (with respect to token content) from at least k other documents in set S (step 460).

In certain embodiments, where a BOW vector is used (i.e., a bag of words vector where “1” means the token is present in the document, and “0” means the token is not present in the document), the bit value in the vector corresponding to an unsafe token is changed from “1” to “0,” and then the unsafe token is later redacted from the document.

3. Method for Document Sanitization

FIG. 5 illustrates a method for document sanitization. The system begins processing an unsafe token (step 510). The system treats the unsafe token as a missing word and uses a machine-learning language model to predict a vector representation of the missing word from the context of the unsafe token within the document (step 520). Examples of machine-learning language models include BERT and word2vec. The system identifies the nearest vector neighbor to the predicted vector representation from the vector representations of the words flagged as safe within the corpus of document vectors (step 530). The system determines whether the nearest vector neighbor is within a threshold distance of the predicted vector representation (step 540). In certain embodiments, the threshold distance is determined using a Euclidean distance. If the system determines that the nearest vector neighbor is within a threshold distance of the predicted vector representation, the system replaces the unsafe token in the document with the word corresponding to the nearest vector neighbor (step 550). In other words, the unsafe token is replaced with a similar word that is flagged as safe. If the system determines that the nearest vector neighbor is not within a threshold distance of the predicted vector representation, the system redact the unsafe token from the document (step 560). The system determines whether there is another token for processing (step 570). If the system determines that there is another token for processing, the system returns to step 510 to begin processing the unsafe token. If the system determines that there is no other token for processing, the document sanitization process is complete (step 580).

4. Example System Architecture

FIG. 6 illustrates an example architecture for a system that performs the methods described herein. However, the methods described herein may be implemented in other systems and are not limited to the illustrated system.

As illustrated in FIG. 6, a client computer 610 communicates with a server 615 over a network. The client computer 610 has a screen/text capture module 620, which is an application running on an agent's computer that captures screen information from a customer service application used by the agent or that captures text from a chat window between users and agents. Information from the screen/text capture module 620 is received at the server API 630, where it is passed to the text sanitization module 640. The text sanitization module 640 performs the methods described herein on the information, using of the corpus of document vectors 645. In certain embodiments, the text sanitization module 640 creates and stores an equivalent vector of cryptographically secure hashes in the corpus of document vectors 645, as well as queries the corpus of document vectors 645 and hashes each word in the queried documents, and stores a mapping of tokens flagged as safe to their language model embedding. The sanitized documents are passed to the database interface 650, which interfaces with and stores the sanitized documents in a database for sanitized text 660.

5. General

The methods described with respect to FIGS. 1-6 are embodied in software and performed by a computer system (comprising one or more computing devices) executing the software. A person skilled in the art would understand that a computer system has one or more memory units, disks, or other physical, computer-readable storage media for storing software instructions, as well as one or more processors for executing the software instructions.

As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above disclosure is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Claims

1. A method, performed by a computer system, for text sanitization, the method comprising: building a corpus of document vectors by performing the following: obtaining a plurality of documents;tokenizing each of the plurality of documents;for each of the plurality of documents, creating a vector representation of the document based on the tokens in the document;building a corpus of document vectors comprising the vector representations for the plurality of documents;obtaining a new document for text sanitization;tokenizing the new document;creating a new document vector based on the tokens in the new document;accessing the corpus of document vectors;filtering each of the tokens in the new document against a privacy threshold, wherein any tokens having a frequency in the corpus of document vectors below the privacy threshold are flagged as unsafe;performing a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors, wherein k is a positive integer, and wherein, during the k-anonymity sanitization process, tokens in the document are flagged as either safe or unsafe;replacing or redacting the tokens in the document flagged as unsafe, wherein replacing or redacting the tokens in the document flagged as unsafe comprises the following for each token flagged as unsafe; treating the unsafe token as a missing word and using a machine-learning language model to predict a vector representation of the missing word from a context of the unsafe token within the document,obtaining a predicted vector representation for the missing word from the machine-learning language model,identifying a nearest vector neighbor to the predicted vector representation from the vector representations of words flagged as safe within the corpus of document vectors,determining whether the nearest vector neighbor is within a threshold distance of the predicted vector representation,in response to the nearest vector neighbor being within a threshold distance of the predicted vector representation, replacing the unsafe token in the document with the word corresponding to the nearest vector neighbor, andin response to the nearest vector neighbor not being within a threshold distance of the predicted vector representation, redacting the unsafe token from the document; andupdating the corpus of document vectors to include the new document vector in its form prior to the filtering and k-anonymity sanitization steps.

2. The method of claim 1, wherein the k-anonymity sanitization process comprises the following: computing a frequency of each token within the document;sorting tokens according to an ordering criteria;identifying a set of documents, wherein initially the set is all the documents in the corpus of document vectors;performing the following for each token according to the ordering criteria: identifying all other documents in the set that include the token;determining if the number of identified documents is greater than k;in response to the number of identified documents being greater than k, flagging the token as safe, and updating the set to include only those documents having the token; andin response to the number of identified documents being less than k, flagging the token as unsafe.

3. The method of claim 1, wherein, for each document vector created, the system creates an equivalent vector of cryptographically secure hashes and builds the corpus of document vectors using the equivalent vectors.

4. The method of claim 1, wherein, for each document, including the new document, the vector representation of the document indicates the tokens present in the document.

5. The method of claim 1, wherein the vector representation includes a first bit value for each token in a vocabulary that is present in the document and a second bit value for each token in the vocabulary that is not present in the document.

6. A non-transitory computer-readable medium comprising a computer program, that, when executed by a computer system, enables the computer system to perform the following steps for text sanitization, the steps comprising: building a corpus of document vectors by performing the following: obtaining a plurality of documents;tokenizing each of the plurality of documents;for each of the plurality of documents, creating a vector representation of the document based on the tokens in the document;building a corpus of document vectors comprising the vector representations for the plurality of documents;obtaining a new document for text sanitization;tokenizing the new document;creating a new document vector based on the tokens in the new document;accessing the corpus of document vectors;filtering each of the tokens in the new document against a privacy threshold, wherein any tokens having a frequency in the corpus of document vectors below the privacy threshold are flagged as unsafe;performing a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors, wherein k is a positive integer, and wherein, during the k-anonymity sanitization process, tokens in the document are flagged as either safe or unsafe;replacing or redacting the tokens in the document flagged as unsafe, wherein replacing or redacting the tokens in the document flagged as unsafe comprises the following for each token flagged as unsafe: treating the unsafe token as a missing word and using a machine-learning language model to predict a vector representation of the missing word from a context of the unsafe token within the document,obtaining a predicted vector representation for the missing word from the machine-learning language model,identifying a nearest vector neighbor to the predicted vector representation from the vector representations of words flagged as safe within the corpus of document vectors,determining whether the nearest vector neighbor is within a threshold distance of the predicted vector representation,in response to the nearest vector neighbor being within a threshold distance of the predicted vector representation, replacing the unsafe token in the document with the word corresponding to the nearest vector neighbor, andin response to the nearest vector neighbor not being within a threshold distance of the predicted vector representation, redacting the unsafe token from the document; andupdating the corpus of document vectors to include the new document vector in its form prior to the filtering and k-anonymity sanitization steps.

7. The non-transitory computer-readable medium of claim 6, wherein the k-anonymity sanitization process comprises the following: computing a frequency of each token within the document;sorting tokens according to an ordering criteria;identifying a set of documents, wherein initially the set is all the documents in the corpus of document vectors;performing the following for each token according to the ordering criteria: identifying all other documents in the set that include the token;determining if the number of identified documents is greater than k;in response to the number of identified documents being greater than k, flagging the token as safe, and updating the set to include only those documents having the token; andin response to the number of identified documents being less than k, flagging the token as unsafe.

8. The non-transitory computer-readable medium of claim 6, wherein, for each document vector created, the system creates an equivalent vector of cryptographically secure hashes and builds the corpus of document vectors using the equivalent vectors.

9. The non-transitory computer-readable medium of claim 6, wherein, for each document, including the new document, the vector representation of the document indicates the tokens present in the document.

10. The non-transitory computer-readable medium of claim 6, wherein the vector representation includes a first bit value for each token in a vocabulary that is present in the document and a second bit value for each token in the vocabulary that is not present in the document.

11. A computer system for text sanitization, the system comprising: one or more processors;one or more memory units coupled to the one or more processors, wherein the one or more memory units store instructions that, when executed by the one or more processors, cause the system to perform the operations of: building a corpus of document vectors by performing the following: obtaining a plurality of documents;tokenizing each of the plurality of documents;for each of the plurality of documents, creating a vector representation of the document based on the tokens in the document;building a corpus of document vectors comprising the vector representations for the plurality of documents;obtaining a new document for text sanitization;tokenizing the new document;creating a new document vector based on the tokens in the new document;accessing the corpus of document vectors;filtering each of the tokens in the new document against a privacy threshold, wherein any tokens having a frequency in the corpus of document vectors below the privacy threshold are flagged as unsafe;performing a k-anonymity sanitization process such that the new document vector becomes indistinguishable from at least k other document vectors in the corpus of document vectors, wherein k is a positive integer, and wherein, during the k-anonymity sanitization process, tokens in the document are flagged as either safe or unsafe;replacing or redacting the tokens in the document flagged as unsafe, wherein replacing or redacting the tokens in the document flagged as unsafe comprises the following for each token flagged as unsafe: treating the unsafe token as a missing word and using a machine-learning language model to predict a vector representation of the missing word from a context of the unsafe token within the document,obtaining a predicted vector representation for the missing word from the machine-learning language model,identifying a nearest vector neighbor to the predicted vector representation from the vector representations of words flagged as safe within the corpus of document vectors,determining whether the nearest vector neighbor is within a threshold distance of the predicted vector representation,in response to the nearest vector neighbor being within a threshold distance of the predicted vector representation, replacing the unsafe token in the document with the word corresponding to the nearest vector neighbor, andin response to the nearest vector neighbor not being within a threshold distance of the predicted vector representation, redacting the unsafe token from the document; andupdating the corpus of document vectors to include the new document vector in its form prior to the filtering and k-anonymity sanitization steps.

12. The computer system of claim 11, wherein the k-anonymity sanitization process comprises the following: computing a frequency of each token within the document;sorting tokens according to an ordering criteria;identifying a set of documents, wherein initially the set is all the documents in the corpus of document vectors;performing the following for each token according to the ordering criteria: identifying all other documents in the set that include the token;determining if the number of identified documents is greater than k;in response to the number of identified documents being greater than k, flagging the token as safe, and updating the set to include only those documents having the token; andin response to the number of identified documents being less than k, flagging the token as unsafe.

13. The computer system of claim 11, wherein, for each document vector created, the system creates an equivalent vector of cryptographically secure hashes and builds the corpus of document vectors using the equivalent vectors.

14. The computer system of claim 11, wherein, for each document, including the new document, the vector representation of the document indicates the tokens present in the document.

15. The computer system of claim 11, wherein the vector representation includes a first bit value for each token in a vocabulary that is present in the document and a second bit value for each token in the vocabulary that is not present in the document.